How to choose a child car seat

Choosing the correct car seat is crucial to ensure your child stays safe – and you stay legal. We reveal all...

best cars for three child car seats

Being a new parent can be stressful, and for many expectant mothers and fathers, choosing the right child seat is a big deal – they’re essential to keep your little one safe, and in the vast majority of cases, they’re a legal requirement, too.

There are countless seats out there, all with different features, a range of prices, and in a number of sizes.

In our complete guide to child seats, we’ll explain how to select the right seat for your needs, how to ensure it’s fitted correctly, and we’ll give our definitive view on whether using a secondhand child seat is a good idea.

We spoke to child seat fitting expert Julie Dagnall of Child Seat Safety, an organisation that holds seat fitting clinics for the public and provides Europe’s only professional qualifications in child seat safety awareness. These are attained by many of the experts that you’ll find when you visit retailers, or if you talk to seat manufacturers. 

Her advice is to “shop back to front”. That means checking out seats on manufacturers’ websites first to find out which is the best seat for your child, then visiting retailer websites to shop around for the seat. 

LT BMW iX3 - installing child seat

“Before you set your heart on a specific seat, check if your car can accommodate it,” she says. “Many seat manufacturers have online car seat compatibility checking tools that let you search for the make, model and year of your car and add the weight, height and age of your child to create a list of seats that will be suitable for use in the car’s various seating positions. Don’t assume the seat will automatically fit, though. In some cases, there will be other issues that can affect fitting.”

There is also a car and seat compatibility tool and fitting videos for many seat brands at child car, the child car seat information website for the Royal Society for the Prevention of Accidents.  

Or, if you’d rather stick with the seats recommended for your car by its manufacturer, you can find out what they are in your owner’s handbook. It’s also worth reading the Euro NCAP crash test results for your car because they provide detailed information about the type of child seat that can be used safely in each seating position, along with the name of the seats used during crash tests.

Which child car seat features should I look for?

Once you’ve narrowed it down to one or two suitable seats, it’s worth doing a bit more intensive research before you buy. Dagnall advises downloading the manual for each seat and reading up on the adjustments you’ll have to make to it as your child grows. For seats that can be used facing either forwards or rearwards, it’s useful to see how much room they’re likely to take up and how they’re secured into the car, in each of the seat's modes. 

5. Child seats

“If you’re not sure about anything, ask the manufacturer for additional information - it’s their product, so they should know it best,” says Dagnall. “Good manufacturers will have a frequently asked questions section on their app or website and customer service helplines on which you can either speak to an expert or have an online chat. Many will also have fitting videos you can watch to help you understand how to correctly install the seat. 

“Alarm bells should start ringing if the manufacturer whose seats you’re looking at doesn’t provide any of these services. We’d recommend only buying from those that have a good amount of information and advice.”

Car seat groups and sizes

All children must use an appropriate child seat until they are either 12 years old or 135cm tall. The seat must comply with one of two EU safety regulations: R44 or R129. 

The R44 standard is an old regulation that separates car seats into groups depending on the weight of the child, and stipulates that children should be kept rearward facing until they are nine months old. 

The newer R129 regulations, which were initially introduced in 2013, categorise seats by a child’s height and state that children should be rearward facing to 15 months. It’s worth opting for an R129 certified seat if you can because they have to withstand more rigorous crash testing than R44 seats. R44 seats are being phased out and will no longer be available to buy from September 2024. 

R44 seats are organised into three different groups. It's illegal for your child to be in the wrong type of seat for their weight.

It's also vital that your child is in the correct seat for their size or they could be inadequately protected and possibly at risk from the seat itself if, for example, the harness were to press on the wrong part of their body in an accident.

R129 child car seat sizes

These seats must be sold with information on the height of the children they’re suitable for. This is intended to make it easier for parents to know when to switch to a larger seat. 

R129 seats come in a range of sizes, but the most common four types are: 

  • 40cm to 85cm child height 
  • 40cm to 105cm child height 
  • 40cm to 125cm child height
  • 40-100cm to 150cm child height

You can read more in our What is i-Size feature.

R44 child car seat sizes

The main R44 child seat groups are:

  • Group 0+ newborn to 13kg (birth to 12-15 months, approx)
  • Group 1 children 9-18kg (nine months to four years, approx)
  • Group 2/3 children 15-35kg (four to 12 years, approx)

You can buy combination seats, which straddle these groupings, and can be suitable from birth right up to 12 years, although you should bear in mind that all child seats have a limited shelf life.

Group 0+ newborn to 13kg (baby seats)

Sometimes called infant carriers, these are rear-facing seats with an integrated three- or five-point harness and a handle so you can carry the baby in the seat outside of the car. Rear-facing seats provide the best protection for a baby's head, neck and spine in a front impact, so avoid moving your baby into a forward-facing Group 1 seat any earlier than necessary.

Group 1 children weighing 9-18kg (toddler seats)

These are chunky, often forward-facing, car seats with an integrated five-point harness. There are some rear-facing models available, providing the benefits of a Group 0+ seat for longer (in a front impact, the child is simply forced against the back of the seat). Other seats rotate, offering the best of both worlds.

Group 2-3 Children weighing 15-36kg (high-backed seat/booster)

These are high-backed booster seats that put your child at the right height to use an adult seatbelt without risk of slipping underneath it or being injured by it in an accident. Guides on the shoulder area and seat base also position the seat belt safely. They have adjustable headrests with wide wings at the top to protect children’s head, neck and upper body in a crash. 

There are also backless booster seats, but these aren’t recommended by safety experts because they provide far less protection for children in an impact. Only children weighing 22kg or more can use a new backless booster seat, but younger children can continue to use an older booster seat if they are already doing so. 

How to fit a child car seat

Although online seat fit checking tools provide a good guide, they can’t take into account all the factors that can affect how suitable a child seat is for a particular car. Here, we outline the most common factors to consider:

Driver and front passenger position

If you or your front seat passenger need to slide their seat back a long way to get comfortable, this could impinge on the space in the back for a child seat. Some rearward-facing infant carriers are designed so the child seat can touch but not push on the back of the front seat, but others need to have a gap of around 10cm between them and the child seat.

Check this with the seat maker and ask them for the seat’s dimensions so you can assess how well it will fit. The same issue could arise if you’re using an Isofix seat base with a support leg; it might need to have a gap between the support leg and the back of the front seat. 


If your car has bulky rear headrests, you might need to raise them upwards or remove them altogether so the back of a forward-facing child seat can sit flush with the rear seatback. Putting a child seat in front of a headrest could compromise its safety by pushing the seat forward and making it difficult to secure using a seatbelt. If you are struggling to find a suitable seat, look for one with a shaped back and an adjustable head restraint rather than a seat with an upright, solid back. 

Number of children 

Best cars for three child seats

If you have two or three children who need to use car seats, you’ll need to find seats that are narrow enough to fit side by side on the rear bench. This shouldn’t be a problem in a large MPV or SUV, but it will be an issue in many smaller cars. Cars that allow three child seats to be fitted aren’t common, but we’ve tested many of the popular models.


Some vehicles have shorter seat belts that won’t stretch around bulkier child seats, so check the length of your car’s belts and the seat dimensions before you buy. Although most newer cars have seat belt buckles that sit flush with the seat bases, some older ones have buckles on long stalks, and this can mean the buckle sits on a corner of the child seat; this compromises safety, because the seatbelt could snap open in a crash. If this is an issue, and your car has Isofix child seat mounts, switch to an Isofix seat so you don’t need to use the seatbelt to secure the seat into the car. 

Seat shape 

The seat bases of some cars are curved, with high side cushions, and it can be hard to fit a child seat securely onto them. To get around this issue, look for a child seat with a small base or one with a separate base and leg support to add extra stability. 

Top tether anchor points 

If you’re considering a child seat with a top tether strap, check your car’s handbook to find out if it has them and where they’re located. Don’t mistake luggage hooks for tethers, because they aren’t fixed to the structure of the car and therefore aren’t as strong. In some older cars, the tethers are hidden behind the upholstery on the rear of the back seats, and you might need to cut the fabric to get to them.

Under floor storage compartments 

Don’t use a child seat with a leg support if it has to stand on an under floor storage box, because the floor won’t be strong enough to support the leg in a collision. Instead, look for a seat with a top tether strap. Some car makers have blocks that can be used to fill up a storage compartment, so check with the manufacturer of your car about this. 

Should I buy a second-hand car seat?

Used child car seats can sound like an appealing and affordable alternative to buying new – but you should resist the temptation because you can never be sure of their history. They could offer reduced protection to your child in the event of a crash.

Additionally, child seats have a shelf life, and by buying used you can never really be sure how old it is. And that could mean it doesn’t adhere to the current safety standards.

A second-hand child seat may outwardly look in good condition, but it’s the internal shell that’s all-important, and any knocks or damage – particularly if the seat is installed in a car that has been in a collision – could compromise its safety. Missing parts, degraded plastics and polystyrene are all also safety concerns.

Child seats are a legal requirement if your child is under 12 years old, or is less than 135cm tall. If you’re on a tight budget, you’re better off buying a new budget seat from a recognised brand than you are buying something second-hand from a more premium manufacturer.

Additionally, you should buy your child seats from a recognised retailer to minimise the likelihood of purchasing an inferior or counterfeit seat.

Should I replace a child seat after an accident?

Parents must renew their child car seat after any collision, even if it's only a low-speed one, according to RoSPA.

Even if there are no obvious signs that a child seat has been damaged, a crash can seriously undermine the structural integrity of a child seat.

One insurer, Direct Line, says the main reason parents give for not replacing a child seat after a crash is that they thought the speed at which the crash occurred was too low to warrant it.

The other reasons are:

• they didn't think they needed to;
• there was no apparent damage;
• they had it inspected but were told it was fine;
• their insurer wouldn't pay for it.

Many insurers will pay for a replacement seat, but you should check with your insurer to be sure.

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