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Baby & child.

22 June 2021

Baby and child car seat safety features

Use our expert car seat safety guide to keep your little one safe. We cover everything from how long a baby can stay in a car seat to when it’s safe to move to the next seat up
Which? Team

Car seats are complicated and you want the safest set up in your car, whether you’ve got a vulnerable newborn, a rambunctious toddler or an older child.

Use the links below to find out the answers to a wide range of baby and child car seat questions.

Once you know what sort of child car seat you're looking for, head over to our child car seats reviews to see the best – and worst – performers in our rigorous tests.

When can a child travel without a car seat?

According to UK law, children need to sit in a car seat up to the age of 12 or until they reach 135cm tall (whichever comes first).

Failure to do this could lead to a fine and points on your licence, and this law extends to anyone transporting someone else’s children in their car as well as their own.

But it’s not a legal requirement to use a car seat if you’re travelling in a taxi (black cab, Uber or minicab).

Download our free guide to car seat law below and go to our guide to child car seat laws in the UK for more information.

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How long can a baby stay in a car seat?

i-Size baby, Group 0 and 0+ car seats are designed to keep your little one safe in the car, not as somewhere for them to sleep for long periods of time.

They position your baby in a semi-supine position (45-degree recline angle) to provide good support for your baby's head and neck, but it can affect their breathing if they are seated for too long.

If your baby is less than a few months old, try not to let them spend longer than 20 or 30 minutes in their car seat without a break. That’s not only when your baby is in a car, but also if the car seat is attached to a travel system pushchair.

Once your baby over six months old, this can be extended to two hours. Do not keep your baby in their car seat for longer than two hours at a time and try to have regular 10 or 15-minute breaks if you’re going on a long road trip.

Is car seat safer behind driver or passenger?

The safest place for your child is in the back of the car, so do always try to fit your car seat in the back.

The back middle seat is generally the safest and can be used, but only if the seat has a three-point seat belt.

Make sure to disable any active airbags in front of your child as they can cause serious injury, especially if your child is rearward-facing.

If you want to put them in the front of the car, make sure the passenger seat is pushed as far back away from the dashboard as possible, disable the airbag for that seat and fit the child car seat securely.

Travel system pushchair with mum and baby

How do you know which car seat is the safest?

Our car seat tests are exhaustive and we carry out hundreds of checks as well as crash-testing car seats to try to find out which are the safest car seats.

Find out more in our guide to how we test car seats.

Go to our best car seats to see the top-scorers that impressed in our crash tests. These are the models that are easy to install and use, as well as being comfortable for your little one.

It’s important to remember that even the safest car seat won’t protect your child properly if it’s incorrectly installed or if your child isn’t buckled in correctly.

Why choose a rearward-facing car seat?

It’s been proven that rearward-facing is the safest way for babies and toddlers to travel. Babies shouldn’t travel forward-facing, and you should never fit a rear-facing child seat in front of an active airbag.

Try to keep your little one rearward-facing until at least 15 months, and ideally up until four years of age with an extended rear-facing car seat.

Your child can then sit forward-facing when it’s time to move to an i-Size child or Group 2/3 high-back booster seat.

Find out more information in our extended rear-facing car seats guide and discover which ones impressed in our tests.

Group 1 car seats

What is the height and weight limit for car seats?

Child car seats are split into groups according to the weight or the height of the child they're intended to protect.

The seats in each group are designed to protect your vulnerable child from crash injuries as he or she grows from a baby to a teenager.

Our guide to car seat weight groups explains the weight limits for group seats conforming to regulation ECE R44.03 or ECE R44.04.

i-Size car seats, which comply with regulation ECE R129, go by height. Your child will outgrow the seat once they exceed the maximum height stated on the car seat’s label. Visit our guide to i-Size car seats to find out more.  

How do you know when it's time to change car seats?

First check what the upper weight or height limits are for your car seat and then measure your child.

Additionally sit your child in the seat to see if your child’s eyes are in line with the top of the car seat backrest, as that means they won’t be getting an adequate amount of protection around their head.

Don’t forget to check if they’re too tall for the car seat harness – the top of it should sit 2cm above their shoulder – even when it’s adjusted to the highest position.

At what age and weight can a child sit in a booster seat?

When your child reaches 18kg or is taller than 105cm (typically around the age of four) you can move them up to an i-Size child or group 2/3 high-back booster seat.

Backless booster seats are only allowed with children weighing more than 22kg or taller than 125cm.

However, we wouldn’t recommend backless booster seats, because they provide no side-impact protection if you’re involved in a side-on collision, and shorter children may find that the shoulder strap of seatbelt doesn’t sit in the right place.

Find out more in booster seats – are you breaking the law?

Group 2/3 car seats

How do I know if my car seat is fitted correctly?

If your car seat sits on an Isofix base with a support leg, make sure it’s still tight and held securely in place.

Many car seats have installation lights and indicators that show red if the seat is not properly fitted and green when it’s correctly installed.

If the seat uses a top tether strap, rather than a support leg, ensure it’s still taut.

Check the manufacturer instructions and look online for any installation videos showing how to fit it.

You can also visit our car seat fitting guide for more fitting information, or consider taking your car and car seat to a car seat checking event.

Are Isofix car seats safer?

If you have a relatively new car (since 2002), it's likely to have Isofix mounting points. This is the standard system for all new cars and seat manufacturers, designed to make installing your child safety seat quick and easy.

Many parents worry about fitting their car seat correctly using the car's seat belt, but with Isofix you simply ‘plug in’ a compatible car safety seat to mounting points in the car – rather than fiddling with seat belts.

Isofix car seats are considered safer as they are easier to install, and as the seat is fixed to your car, they can hold the car seat more securely than using the car's seat belt.

Visit our guide to Isofix car seats to find out more.

What’s buckle crunch and why is it bad?

Only the seatbelt webbing should touch the child car seat's frame, not the buckle.

Otherwise pressure on the buckle could make it fail, meaning your child won’t be securely restrained in an emergency situation. Check the child car seat’s fitting manual for more information.

Is it safe to use a car seat without the base?

Not all car seats can be used without an Isofix base, but some allow a belted installation.

Check the instruction manual or our car seat reviews to what installation methods are possible for your car seat.

You cannot attach a car seat without the base if the instructions prohibit this.

Should my car seat move side to side?

The car seat should sit firmly and securely on the back seat of your vehicle.

Check your car's head rest won't interfere with getting a snug fit for your car seat. If the head rest is getting in the way, either pull it up out the way or remote it altogether.

If your rear seats slope down from front to back and towards the middle, it might mean the car seat doesn’t sit flush with the vehicle seat. Don’t place anything beneath the child car seat to adjust this (a blanket, for example), but contact your car and car seat manufacturer for advice.

Go to our car seat fitting guide for more fitting information.

Is there any way to tell if a car seat has been in an accident?

The short answer is no. Although a car seat may look fine, there is no way to tell if it’s been compromised. Even a small hairline crack in the shell could mean it doesn’t provide the protection it’s meant to in the event of a road collision.

Mum strapping child in car seat

What should your child not wear in a car seat?

Don’t be tempted to strap your child in with their coat still on.

Bulky clothes or puffy all-in-ones should be removed to ensure you get a tight fit on the harness. Tuck a blanket lightly over your baby and toddler once strapped in if you’re worried they’ll be cold.

How do I know if my car seat harness is tight enough?

Check that the harness is roughly level with your child’s shoulders, and the straps secured tightly over their body – tight enough so you’re just able to fit two fingers between the shoulder straps and your child’s body.

This is to ensure your child is held securely, and there’s no room for their shoulders to slip out and risk them being thrown out of the car seat.

Before setting off, make sure the harness isn’t twisted at all and there are no worn or frayed areas.
Installing a child car seat

Can I use car seat accessories with my car seat?

Unless they’re designed and tested by your car seat manufacturer alongside your seat, we’d advise against using car seat accessories.

There’s an enormous array of cheap products – often available via online marketplaces – that claim to solve car seat issues that parents may encounter on long car journeys.

These include head straps to prevent slumping and harness buckle covers to stop your baby unclipping themselves.

Read our guide on car seat accessories to find out which ones should be avoided.

Car seat cleaning

Do I need to clean my car seat?

Yes we’d recommend cleaning your car seat as it will become a magnetic for germs.

Before you start, read the instruction manual to check how to remove the seat cover, and take photos as you go so you remember how each part of the seat is set up.

The care labels on the cover will explain how it can be washed (machine or hand wash), but the harness usually needs cleaning separately with a brush so you can scrub it.

During our testing, we check how easy car seat covers are to remove, and give them a cleaning star rating, so look out for seats that score well in our reviews.

Is it safe to have three car seats in a row?

In this instance the size of the car seats and the space in the rear of the car may be an issue.

If you have lapbelt seat belt for the middle rear seat, rather than a standard three-point seat belt, then it can't be used to attach a car seat. In this instance you would only be able to fit two car seats in the rear.