Our main recommendation
We rate the Philips Sonicare for Kids Connected as the best electric toothbrush for children aged 3+.
In this post we explain how we came to this decision, and offer some alternative options should you be looking for something slightly different.
Our in-house dentist Dr. Gemma Wheeler explains the evidence for children using an electric toothbrush, and our buyer’s guide includes further advice to help you decide.
In this post
Key tips for looking after your child’s teeth
Creating a regular brushing habit with your child is important. It’s more important than the toothbrush you choose.
Getting kids to brush their teeth at all, let alone correctly, can be a real challenge. Here at Electric Teeth, we are parents too. We know these difficulties all too well and we empathise with you.
Don’t worry if things don’t go to plan every time.
It is better to have a quick brush than nothing at all. Skipping the odd session might also be unavoidable. It is better this way than brushing becoming a negative experience for them.
Focus on making tooth brushing a positive experience.
Work towards achieving the following with your child:
- Brushing their teeth twice a day with an age appropriate fluoride toothpaste
- Brushing their teeth for 2 minutes each time
- Using the correct brushing technique (if possible)
- Having them spit the toothpaste after brushing, rather than rinsing with mouthwash or water
- Taking them for regular dental checkups
You should encourage independent brushing. However, children should be helped to brush, or supervised, until they are around 7 years old.
If you can encourage them to clean between their teeth once a day this is very beneficial too. You can try using floss or interdental brushes.
Creating a regular brushing habit with your child is important. It’s more important than the toothbrush you choose.
Dr. Gemma Wheeler, BDS (Hons)
Is it safe for a child to use an electric toothbrush?
Yes it is, providing your child is supervised when they brush. You should do this until they are 7 years old.
Research is lacking, but one specific study showed no damage to teeth and gums when children used an electric toothbrush.
Try to use an electric toothbrush designed for children as opposed to an adult brush. This is because the handle and brush heads have been designed with the needs of a child in mind.
Can an electric toothbrush replace a manual toothbrush?
Plaque is one of the key reasons we brush our teeth. It needs to be removed to reduce the chance of decay and gum health issues.
The electric toothbrush appears to encourage longer brushing times. This allows for more plaque removal.
A manual toothbrush is adequate if your child complies with regular brushing sessions.
Can an electric toothbrush improve a child’s oral health?
Children using an electric toothbrush will remove more plaque, reducing the risk of gum disease and decay.
Although children will lose their first set of teeth, the health and condition of these teeth have an impact on their permanent (adult) teeth (1). Poor dental health in children is also linked to poor school attendance (2) and poor general wellbeing.
Promoting regular oral care at a young age is important for developing good habits later in life.
Do dentists recommend electric toothbrushes for children?
Although it is not essential, I believe an electric toothbrush is a great tool to help children when brushing their teeth.
I want a child to enjoy their experience. I want them to want to brush twice a day, every day. And in time, I want them to learn why it is important to take care of their teeth.
The bold coloured handles, characters and games these brushes offer, grab the child’s interest and attention.
The clinical evidence is limited, but what exists does show that children will brush for longer and remove more plaque.
My own experiences confirm this to be true.
I also find that both the parents and child see the act of toothbrushing more positively when switching to an electric brush.
What to look for in a kid’s electric toothbrush
There are lots of children’s toothbrushes to choose from.
From our testing, the most essential features to look for in an electric toothbrush are:
2 minute timer
A timer helps to ensure that you brush your teeth for 2 minutes each time, which is recommended by dentist and governing bodies around the world.
Colourful / engaging handle design
Engaging brush handles capture the child’s attention. Most toothbrushes for kids have this box ticked, but you need to be considerate for your child and what colours and characters motivate them.
Little hands can struggle to keep hold of some items, especially if they are wet. The more silicone/rubber on the handle or textured surfaces, the better.
How much should you spend?
Our number 1 choice is one of the more expensive electric toothbrushes for children.
When factoring in what it offers, it is the best brush to invest in.
You can get very good brushes for less money. But, they don’t offer quite the same complete package.
A little extra spent at the outset can go a long way in creating positive brushing experiences.
In most instances, a good kid’s electric toothbrush is going to come in at well under $40.
There are many that cost a lot less. They usually have the key features you need. But, they might not offer quite the same ‘complete package’ that you get with some others.
How we chose
Our selection process
Our team is made up of dental professionals and experienced product testers. We specialise in oral health and abide by a strong code of ethics.
As parents ourselves, we test these products with our children. They are some of the hardest to please at times!
We buy and test every product we recommend. In most instances, we have detailed written and video reviews for each product.
We consult the clinical evidence, the feedback from consumers and industry leaders.
Together, we ensure our recommendations include only the very best choices.
We regularly review our recommendations, based on product availability and clinical evidence.
Best electric toothbrush 2021 — our recommendations
In the sections below we go into detail about the kids brushes we have tested and explain our recommendations.
Dr. Gemma Wheeler also answers common pre-purchase questions.
Sonicare For Kids Connected
*Prices correct at time of writing
Why we chose it:
The Sonicare for Kids Connected is an expensive option, but your child will love using it.
Replaceable stickers on the front capture your child’s attention. They feature ‘Smiley’ – a loveable character. He teaches good oral care habits within the app, which is well designed.
The smartphone app works in real-time with the brush. It explains and demonstrates why brushing is important. Kids win prizes after brushing sessions to feed and customise Smiley.
The handle is really grippy. The rubber coated brush head is soft on your child’s teeth and gums.
There are two different brushing intensities to choose from, which is useful as you can test both to see which works best for your child.
It offers weeks of use on a single charge. You get an audible and vibrating warning when it needs charging. You don’t need to worry as much about keeping it topped up compared to rival brushes.
What we like
- 2 minute timer
- Colourful/engaging handle design
- Grippy handle
- Long battery life
- 2 cleaning modes
What we dislike
Oral-B Stages Power
*Prices correct at time of writing
Why we chose it:
The Stages Power has the essential features required of a kid’s electric toothbrush.
It is a good value option.
The large textured grips help you and your child to hold securely onto the brush.
The bold colours and Disney characters will get your child excited. The optional smartphone application can be customised to match the brush characters. The on-screen timer can help educate them to brush for 2 minutes. The brush and app are not connected with Bluetooth, which means they are not in sync with each other.
The small round brush head is easy to move around your child’s teeth.
Unfortunately, the battery life isn’t very good. The lack of a battery status light means you get little or no warning if the battery is flat. You have to keep it topped up to stop this from happening.
What we like
- 2 minute timer
- Colourful/engaging handle design
- Grippy handle
- Good value
What we dislike
- Short battery life
- The brush does not connect via Bluetooth to the smartphone application
Recommendations by age
Many people ask what is the best toothbrush for children of a certain age.
The following table lists our recommendations by age along with some useful notes.
Please be aware children develop at different rates. What might be right for one, might not be for another.
When transitioning a child from a kid’s to an adult brush head or toothbrush, be sure to assist them and monitor their responses and act accordingly.
Some will find the size and power too much whilst others will be very comfortable with the switch. Introduce them when you as the parent or guardian feel they are ready. Don’t be afraid to take a step back if necessary.
|Age (Years)||Best Electric Toothbrush||Notes*|
|0 – 2 year old||Require a baby toothbrush|
|3 – 5 year old||Philips Sonicare for Kids Connected||Assist/oversee the child’s brushing|
|6 – 7 year old||Philips Sonicare for Kids Connected||Can potentially switch to an adult round brush head such as those form Oral-B.|
Opt for the soft/sensitive heads & use a gentle cleaning mode.
|8 – 11 year old||Philips Sonicare for Kids Connected||Can move to an adult brush head, be that round Oral-B or larger sonic brush heads from Philips.|
Opt for soft/sensitive bristles.
|12 – 14 year old||Oral-B Pro 2 2000||Move to adult toothbrush|
* Rough guidance only, always consult a dental professional.
Our choices explained
The Sonicare for Kids Connected electric toothbrush is a clear top pick for us.
Yes, there are some other great options, but the complete package on offer makes the Connected a winner.
It is more expensive than most other brushes. But, that cost seems very well spent when you see the enthusiasm your child has for brushing.
The colourful monster-like character called ‘Sparkly’ plays an important role. He adorns the stickers that can be placed on the front of the brush handle. He is then their guide through the very well designed smartphone app.
We don’t like to encourage more screen time than is necessary, nor phones in the bathroom, but it works so well here.
The Bluetooth connection ensures the brush handle is in sync with the timer. Your child can’t say they have brushed for 2 minutes when they haven’t!
Before brushing there is a quick educational piece about the importance of looking after the teeth. Don’t worry, this can be skipped if you are short of time.
This is then followed by great on-screen visuals of Sparkly brushing his teeth. He talks about removing the bugs to get them clean. It’s filled with motivational messages. Plus, because the app and brush are in sync, it tells your child when to move from one area of the mouth to another. The handle vibrates too.
A successful brushing session is rewarded with presents. This can be food for Sparkly or accessories to dress him.
Every child is of course different. But we have seen how different our children have reacted to using this compared to a manual brush.
The Oral-B Stages Power is a more affordable option. It should not be overlooked. It has the essential features covered and does what it needs to do.
Kids do like to open and close their mouths with no particular pattern when brushing. Not to mention struggling to work out where to put the tongue. Oral-B’s small round brush head is good in this situation as it is easy to move around the mouth.
We like the blue indicator bristles on the brush head that show how much toothpaste to use. Or rather, how little you actually need.
Brush heads are interchangeable. They can be swapped out for an adult/larger brush head as and when is appropriate.
The battery life isn’t very good and you get no indication of the remaining power. It is all too easy to forget to put the brush on the charging stand and find it is flat come the next brushing session.
The free Disney Magic app is useful and educational for your kids. The problem here is that the toothbrush is not in sync with the brush. So in theory, the child could start the timer on the app and not brush at all for 2 minutes. If you are supervising then this is less of an issue, more something to be aware of.
Other kids brushes we have tested
The vast majority of toothbrushes for children are actually manual brushes. These are adequate, but as we have highlighted above there are some extra benefits to going electric.
Some models are designed for different age groups. What appeals and works well for one might not be quite the same for another.
By the age of 8, children can start progressing to adult electric toothbrushes. In fact, Oral-B have models for those aged 6+ that have the same sized brush head as their adult toothbrushes.
One such example is the Oral-B Junior (view it here on Amazon). It is available in 2 colours — purple and lime green.
Aside from the colour of the handle, there is nothing that appeals to children, which is a bit of an oversight. Come 6 years old they do tend to be quite independent, but some extra incentives would be good.
To be fair, it cleans the teeth well and is easy to use. It comes with a soft bristled brush head. It has a built-in timer and pacer and is slim in hand.
You do get a battery status light, unlike the Oral-B Stages Power. The battery lasts for about 7 days from a single charge, which isn’t much better than then Stages Power. And, although there are grips on the rear of the handle, they are hard plastic. They are not softer rubber/silicone, which we prefer.
A winning factor is that it is affordable and easy to keep clean.
Brusheez electric toothbrush (view it here on Amazon) isn’t Bluetooth enabled. There is no smartphone app.
Instead, it comes with a stand that includes a sand timer.
Your child can turn the timer to see the sand pass from one chamber to the other. It is a great way of educating them on the importance of brushing time.
There are a few different styles of handle available, all with animal themes that are engaging. Each one has its own name. For example Ollie the elephant.
The handles are a bit plasticky, which is to be expected. There are raised elements to the handles which help with grip. But there are no softer rubber/silicone pieces which is a shame.
They come with a brush head cover and an easy to use on and off button.
Both the brush head and the batteries are replaceable. It is powered by 2 x AA batteries.
Removable batteries can be beneficial, although long term ownership costs can sometimes end up being more.
Brush-Baby’s KidzSonic toothbrush (view it here on Amazon) is a pretty solid offering.
Powered by 1 x AAA battery, it is replaceable and comes with a battery in the box.
The small brush head is nice and easy to move around the teeth of your child. The bristles are soft too. Some bristles are longer whilst some are shorter. These target either the tooth surface or between the teeth.
We have been impressed with the cleaning results and do also like the fact you get 2 heads included in the box.
There are 2 different power modes. This allows you to adapt the intensity to suit your child. There is a timer and pacer built-in as well.
A disco-style light flashes up through the clear shaft of the brush head, making it fun for your little one.
Small and lightweight, the handle comes in 6 different designs too.
The Colgate Kids Minions brush (view it here on Chemist Warehouse) initially looks like a nice choice. The Minions characters are engaging along with the striking red and yellow colour scheme.
The big problem here is that the brush head is not replaceable. Yet the batteries are.
This is encouraging excessive use of the brush head. Bristles wear out over time and need to be replaced. It is a very wasteful approach and not at all environmentally considerate.
On top of this, the build quality and reliability is an issue. It feels relatively cheap. Many parents complain of this failing within weeks of purchase.
Another brush that falls into a similar trap is the Oral-B Stages Power (the version with removable batteries). Yes, confusingly, this is the same name as our budget choice. It is different in its features and design.
The design of the handle is very appealing to the age group. There are bold colours and different Disney characters available, depending on the variant. For example, Frozen or Star Wars.
It appears to do a good job of cleaning the teeth and the bristles are nice and soft.
In this instance, neither the brush head or the batteries are replaceable. This is very wasteful and not something we can endorse.
A new type of toothbrush is the mouthpiece or automatic toothbrush. These are products that clean multiple tooth surfaces at once. The most popular options, clean all the teeth at the same time. One of the benefits is a shorter brushing time.
Products like the Autobrush for kids look and sound very appealing on paper. They have an interesting design and play sounds to engage your child. For particular kids, such a product can be helpful on their journey to better brushing. The problem here is as yet they are not suitable replacements to a regular manual or electric toothbrush. They don’t clean the teeth well enough and we strongly advise you avoid them.
Useful pre-purchase advice
Dr. Gemma Wheeler, BDS (Hons)
With the help of our in-house dentist Dr. Gemma Wheeler, we’ve added useful notes and tips from our research and testing.
No doubt you’ll have one or two particular questions before buying, as did we.
Browse the sections below, and if you can’t find the information you need, please leave a comment at the bottom of this page and we’ll get back to you.
What are the pros and cons of an electric toothbrush for kids?
We have already explained that you can use an electric brush instead of a manual one, and have supported this with evidence about how an electric toothbrush can improve your child’s dental health.
But what are the other pros and cons of choosing an electric toothbrush for your child? This list is a combination of evidence we have already discussed and the professional experience of our in house dentists.
|Less technique sensitive||More expensive than a manual toothbrush|
|Remove more plaque||Need a power supply to recharge (or access to new batteries)|
|Easier if you have limited hand movements||Need to buy matching replacement brush heads|
|Easier for people with braces||Not as travel friendly because they are bigger and can turn on in transit|
|More likely to brush for 2 minutes||More susceptible to damage|
|Bluetooth technology teaches better habits and help track brushing progress||Some children don’t like the intensity and sensation of the cleaning action they provide|
|Apps gamify the toothbrushing experience to make it more fun and enjoyable.||Negative impact on the environment|
|Pressure sensors prevent brushing too hard and potentially damaging teeth and gums||Need to be disposed of as electrical waste|
Is it better to choose an electric toothbrush instead of a manual toothbrush?
Yes, an electric toothbrush is better than a manual one. The exception to this is if your child has a perfect manual toothbrushing technique.
For children in particular, it is difficult to get the right technique with a manual toothbrush. They do not have the motor skills to be able to brush effectively. One study found that even in 12 year olds with professional teaching, the actual effectiveness of brushing is limited.
Electric toothbrushes make it easier to get a good cleaning technique. They are proven to help improve your dental health, including gum disease, bad breath, and reducing the risk of tooth wear.
The benefit comes from the number of brush strokes. On average, a human generates 300-600 brush movements per minute with a manual brush. By contrast, it is possible for electric toothbrushes to do 62,000 movements per minute.
Even the Oral Health Foundation has acknowledged how powered toothbrushes can help make brushing fun and make sure your child brushes for the correct amount of time.
There is actually little evidence against the use of the electric toothbrush.
Yes, manual toothbrushes can be good enough. But they rely on the person using it to brush properly.
These studies generally say there is no evidence that electric toothbrushes are definitely better. But they do recognise that most people do not have a good enough brushing technique. They didn’t look specifically at brushing techniques of children.
When looking at studies focused on children, they all promote the use of an electric toothbrush over a manual toothbrush.
A review of the existing clinical data by Davidovich et al concluded the powered toothbrushes were more effective at removing plaque than a manual brush.
This study showed children using electric toothbrushes removed 40% more plaque.
Purushotham et al looked at the impact of plaque removal, when a parent brushed their child’s teeth with either a manual or electric toothbrush. The results confirmed the findings of others. There was significantly better plaque removal when a parent used an electric brush.
When it comes to adult studies, an 11 year study by Pitchika et al examined the long term successes of electric toothbrush users. It concluded that use of the electric toothbrush has a positive long-term effect on oral health. Gums were healthier and electric toothbrush users lost fewer teeth.
As well as being better at cleaning, an electric toothbrush will help your child develop better brushing habits.
An electric toothbrush can help teach correct technique, set reminders to brush twice a day, and make the experience more fun.
A toothbrush that encourages your child to brush twice a day for two minutes each time, is always going to be better than the one they won’t use.
Should I make my child use an electric toothbrush?
We don’t ever advise forcing your child to use an electric toothbrush.
But you can encourage them to use one if you feel it will have beneficial results for you and them.
As we have shown, particular brushes will likely engage your child. They will want to use it once they are shown how.
If your child doesn’t get on with an electric toothbrush, don’t worry. Some find the brushing sensation odd or too powerful.
Their tastes and tolerances will change as they grow up.
There are parents on our team, and we have switched between manual and electric at times.
Regardless of how the brush is powered, it is important to ensure toothbrushing is regular.
Everyone’s individual circumstances are different. It is always worth asking for advice from your dental professional.
Is a smart / Bluetooth enabled toothbrush worth it?
If we were talking about adult toothbrushes, then no.
However, with children, the answer is yes, in most instances.
Children don’t know what a good oral care habit is. They need to be shown and taught it.
As a parent, you can play a pivotal role in this. But, you know how stories with interesting or familiar characters capture your child’s attention. As do the bold colours.
Smart toothbrushes for kids gamify the experience. They aim to make it more fun and enjoyable and get kids brushing for longer.
They don’t focus on how well the child has brushed. They work to get your child excited about brushing again and again.
These are examples of how some screen time can be positive.
Does my child need to play a game on my phone when brushing their teeth?
A child does not need to play a game on your smartphone when brushing their teeth.
Yet research has shown that doing so can help encourage regular toothbrushing.
Children learn well through play and repetition. Apps can gamify toothbrushing and encourage kids to enjoy it.
Numerous independent studies have shown how electric toothbrushes encourage users, including children, to brush for longer.
Not all children will be motivated by this. As a parent, you can explore what motivates and encourages your child.
The more fun and engaging it is, the more likely oral care will become a regular habit.
A quick explanation of the types of toothbrushes available for kids
There are 2 main types of electric toothbrush, sonic and oscillating-rotating.
Another type of toothbrush is an ultrasonic brush, but these are not available or suitable for kids brushes.
Sonic or oscillating, they both clean the teeth and gums. They just use slightly different techniques to get the results.
Although it can be worthwhile understanding the differences, don’t centre your decision around this. You have more important things to worry about with your children’s oral health.
Both types have a mechanical cleaning action. This is where the bristles move over the tooth and gum surfaces. This removes plaque by essentially sweeping and scrubbing the surfaces.
Sonic toothbrushes use a mechanical side-to-side motion of the bristles to physically remove plaque. They have an additional cleaning motion as the sonic technology is able to disrupt plaque below the gum level.
To be effective, the brush head must vibrate at frequencies that humans hear (20-20,000hz). This intense vibration agitates fluids that surround the teeth. This disrupts dental plaque in places where the bristles do not reach.
Oscillating-rotating toothbrushes also clean the teeth in 2 ways. The mechanical cleaning action is from side to side movements in a circular motion. To get a deeper clean, there are 3D high frequency pulsations (vibrations) that agitate fluids that surround the teeth. These can loosen and remove dental plaque in locations that are beyond the physical touch of the toothbrush.
Sonic toothbrushes are most commonly associated with Philips Sonicare whereas oscillating toothbrushes are more commonly associated with Braun Oral-B.
Other brands now use both technologies. It is the sonic type of toothbrushes that are most widely used outside of the Sonicare brand.
Both types can be powered by built-in or removable batteries.
Mouthpiece toothbrushes are a new style of brushing. Some even have children’s sizes. They also use a mechanical cleaning action, whereby the bristles make physical contact with the teeth and gums. They have a U shaped mouthpiece, which you bite down on. There are then bristles or silicone filaments coming off this section to cover teeth on both the upper and lower arch. A central motor supplies the power to cause the bristles or silicone filaments to move from side to side.
The concept is to apply cleaning movements to all surfaces at the same time. There is no evidence to support their claims. In fact, one study reports them as being as good as no brushing at all! We do not recommend them.
What makes a good children’s electric toothbrush?
There are only a few basic elements that are needed to make a good electric toothbrush for kids.
Many can be far more complicated than they need to be. But, some of these extra features can bring advantages.
We feel the most important features are:
2 minute timer
We cannot stress the importance of a timer enough.
Dentists, hygienists and governing dental bodies around the world are in unison here. They agree that brushing your teeth twice a day for 2 minutes is important.
A timer keeps track of how long the toothbrush has been switched on for.
At the end of 2 minutes (120) seconds, the toothbrush will either power off or briefly pause the brush motor to alert the brusher that 2 minutes have passed.
2 minutes can feel like a very long time for children. They are certainly not going to brush for 2 minutes all the time.
The timer helps keep them on track though. Over time they will learn that if the timer hasn’t gone off, they haven’t brushed for long enough.
It helps encourage them as they develop toothbrushing skills.
Colourful/engaging handle design
As important as tooth brushing is, it needs to be fun and engaging for the child.
Colourful brush handles capture the child’s attention. Some will have popular TV or movie characters on them too. They can potentially feel gimmicky or overkill. But they can be worth their weight in gold, if it makes brushing more enjoyable.
This is most important from the ages of about 18 months through to about 7 or 8 years old.
Younger or older than this, then it is a little less of an issue.
Most toothbrushes for kids have this box ticked. But, you need to be considerate for your child and what colours and characters motivate them.
Little hands can struggle to keep hold of some items.
Toothbrushes easily get wet and have toothpaste and saliva drip down them. This makes them slippy in hand and even harder to hold onto.
If the toothbrush is all gloss plastic, with no lumps bumps or grippy materials, it is going to be dropped.
The more silicone/rubber on the handle or textured surfaces, the better. As long as the child can still wrap their hand around the majority of the handle.
An explanation of the different brush heads
There is a limited choice for kids brush heads. This is a good thing.
Oral-B offers a small round kids brush head. It is fractionally smaller than their adult heads. There is just 1 style of kid’s head. This smaller head suits children aged under 8 perfectly well. Although from about 6, you could transition to an adult head. Do monitor your child’s comfort with using the larger head. Make sure the head has soft bristles.
Sonicare offers a compact and a standard sized kids brush head.
The compact is the smaller of the 2. This is great for younger children aged 3-4 who have smaller mouths. It is the standard sized head that is most common and easier to source.
As with the Oral-B head, you can switch between the 2 sizes when you feel it is right for your child. Do ensure they are comfortable with the switch and it suits them ok.
Cost of replacement brush heads
The cost of replacement heads affects the long term ownership cost. It is worth factoring into your decision. Oral-B brush heads are cheaper than Sonicare as a general rule.
It’s recommended that you replace your child’s toothbrush head every 3 months. If you follow that advice you’ll need 4 brush heads a year.
Official brush heads cost anywhere from about $7-12+ per brush head. This can be a lot of money when they will only be thrown away 3 months later.
You can save money by buying when there’s a deal on or by buying in bulk.
Do be mindful of the age of your child and how many brushes you will need over the coming months/years. You don’t want to be stuck with lots of smaller brush heads when they have transitioned to an adult toothbrush.
In most instances, you have the choice of opting for a third party brush head. There may not be the same range and the quality may be different. But there are some great options at very good prices.
Do be aware of fakes/counterfeit brush heads which pose as genuine but are often not the real deal. If the price is too good to be true, it probably is.
In the video below our chief product tester Jon Love explains the advice from our buyer’s guide and runs through our choices for the best kid’s electric toothbrush.
How to use a kid’s electric toothbrush
There are right and wrong ways to brush teeth.
With young children, the technique isn’t quite as important — it’s more about the act of doing something and building a routine.
For children under about the age of 5, you want to be getting them to brush for 2 minutes twice a day.
The following video will help them learn why and show them how to brush:
If you can introduce the correct technique, this is going to have benefits.
By the age of about 5, you should be working to make the technique central to your child’s brushing routine.
You will need to continue to go over your children’s teeth to make sure they are fully cleaned, until your child is about 7 years old. This is because they often miss areas.
Encourage brushing each section of the mouth evenly and with the bristles at 45 degrees to the gumline.
We have a detailed guide available, which explains how to brush your teeth properly. It is geared to adults, but you can relay it back to your child.