9 things I'd never do as a car seat expert

Which? has been testing car seats for more than 50 years. Our tests and reviews have been helping to raise the standard on car seat development by testing beyond the legal regulations and encouraging manufacturers to create products that can meet our tests.

Along the way, our work with laboratory experts, car seat fitters and retailers means we've picked up plenty of expertise and inside knowledge – and we want to share that with parents, grandparents and carers. 

Watch the video above and read on to find out more.

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1) Never use an R44 car seat

The R44 car seat regulation is the older of the two current car seat regulations operating in the UK. 

R129 is a newer regulation and was introduced in 2013 to run alongside R44. 

While car seats approved to both regulations are legal, the seats approved to R129 go through crash tests at higher speeds and include a side-impact test, which the R44 tests do not. The R129 tests use Q dummies (rather than the P dummies used in R44 tests) with more sensors to measure forces on a child's body when the car seat goes through a crash.

Fewer R44 car seats are being launched these days, so if you spot one for sale, it's likely that it's been on the market for a while. And while it should be safe, it may not have all the benefits of new car seat technology and development.

What are the key differences between R44 and R129 car seat regulations? We compare i-Size car seats with older group 0, 1, 2 or 3 car seats

2) Never turn your child's car seat forward-facing too early

If you're using an R129 i-size car seat, you shouldn't turn your child forward-facing until they're 15 months old, which is usually when they're 83-87cm tall. 

While manufacturers are taking steps to reduce this risk by putting mechanisms into car seats that prevent you turning or clicking the car seat into a forward-facing position too early, there are others that don't have this option. 

In our car seat reviews, we'll flag if there's a risk that a parent could turn the seat around too early.

We'd recommend you keep your child rear-facing for as long as possible, as it's the safest way for them to travel. There are lots of extended rearward-facing car seats on the market now, which let you keep your child facing backwards up until the age of four (and even older in some cases).

Read our best extended rear-facing car seat guide for more information.

3)Never use a second-hand car seat

A second-hand car seat bought from an online marketplace such as eBay or Facebook marketplace may seem like a bargain, but you can't guarantee that it hasn't previously been in a crash.

There may be hairline cracks or internal damage within the workings of the car seat that aren't immediately obvious, but could mean that it wouldn't adequately protect your child if you were in a collision.

Car seats can be expensive, but they're among the few baby items that we recommend you buy new. You don't always have to spend a fortune – use our cheapest Best Buy car seat reviews filter to help you pick a lower-priced model.

What should I do with my old baby car seat? Find out the best way to dispose of a car seat you no longer need

4) Never strap in your child while they're wearing a puffy coat

Don't strap your child into their seat while they're wearing a puffy coat or snowsuit as it can stop you getting a tight enough fit on the safety harness. 

This is especially noticeable in a crash, when the forces compress the puffy padding so much that it can mean your child slips out of the harness and is thrown from the seat.

Instead, follow the 'strap then wrap' rule. This means strapping your baby into their car seat, and then wrapping or tucking a blanket over them to keep them warm.

5) Never use a backless booster seat

Crash tests have shown that they don't provide the same level of protection in a side-on collision compared with a high-backed booster seat. 

Backless booster seats are still legal, but any made and sold since March 2017 can only be used for children taller than 125cm or weighing more than 22kg. Booster seats made before this date can still be sold and used by children weighing 15-36kg, but we wouldn't recommend this.

The only time we'd suggest using a backless booster seat is if it's a choice between that and not using one at all. 

For example, if you're travelling in a taxi that has no car seat provided, a backless booster seat would provide more protection than simply sitting your child on the vehicle seat and strapping them in with the seatbelt.

Read our guide on high-backed and backless booster seats for further information.

6) Never move your child to the next seat size up before they're ready

It's better and safer to keep your child in the lowest-group seat for as long as possible, rather than moving up to the next group too early. 

Keep an eye on your child's height (for R129/i-Size car seats) or weight (for R44 car seats) so that you can move them up when the time is right, but not before.

Bear in mind that car seat size limits can overlap. For example, a baby-to-toddler car seat might be approved for use from when your child is 40cm to 105cm, but the next size up (a child car seat) starts from 100cm. In this case, keep them in the toddler seat until they're 105cm, and then switch to the next child car seat.

Our guide on car seat height and weight groups has advice and other signs to look for to help you know when it's time to switch seats.

7) Never forgo a car seat when transporting other people's children

In the photo above you can see that the middle child is not wearing their seatbelt correctly. UK car seat law states that it's the driver's responsibility to ensure ALL children up to the age of 12 or 135cm tall (whichever comes first) are sitting in a car seat and properly restrained when you're driving. It doesn't matter if they're not your child, or you're only travelling a short distance.

If you're helping a friend with a school drop-off or pick-up, make sure you have all children travelling in the car strapped properly into a car seat.

Failure to comply can result in a £500 on-the-spot fine if police catch you.

Familiarise yourself with all the UK child car seat laws to make sure you don't get caught out.

8) Never leave a newborn in the car seat for too long

Babies need regular breaks from being in their car seat and the frequency of stops will depend on their age. Newborns should get a break from their car seat every 20 minutes, while for while older babies it's every two hours.

According to the Lullaby Trust, the safer sleeping charity, there has been research into the link between car seats and a risk of breathing difficulties due to being in a seated position.

It’s OK for your baby to fall asleep in a car seat when travelling, but they should be taken out as soon as you get to your destination, and placed onto a firm, flat surface to continue sleeping.

Some car seats offer recline options that put your baby in a nearly flat position (at least a 150-degree angle) but we'd still recommend regular breaks during car journeys.

Lie-flat car seats we've tested and reviewed include the Maxi Cosi Marble, Joie i-Level and Britax Römer Baby-Safe2

9) Never ignore or throw out the manual

It's vital that a seat is correctly installed. The best seats will have simple and clear instructions that make it easy to fit, with a low risk of doing it wrong. 

Even if you've had your car seat installed by a professional retailer or fitting service – something we highly recommend – you should still hold on to the instruction manual in case you use the car seat again for a second sibling and need to reinstall it at a later date.

Some manufacturers only provide online manuals, which you can access via a web link or QR code on a slip of paper or leaflet, so hold on to this too.

If you're unsure, look for guidance from the manufacturer or take your seat to a car seat checking event.

Follow our tips and advice on how to fit a baby or child car seat