Car seats for older children: high-back vs backless booster seats

UK law states that children must use a child car seat until they're 12 years old or 135cm/4ft 5in tall, whichever comes first. From around the age of four, this usually means either a backless booster seat or high back booster.

A booster seat is a backless car seat cushion that raises a child around four to six inches above the vehicle seat so that the three-point seat belt sits across the correct places of a child's body so that they're restrained safely in a crash. 

A high back booster seat has the same seat base as a backless booster seat, but it also has a back and side wings that surround the child and protect their head and torso from side-on collisions.

Our experts don't recommend backless boosters because of serious safety concerns, as we explain below.

Read on to find out more about car seats for older children, or head straight to our reviews of group 2/3 or i-Size child car seats to pick the best

Best high back booster seats

What are the best child car seats for tall children?

If you want to keep your child in a child car seat for as long as possible for safety reasons, but they’ve reached or exceeded the 135cm/4ft 5in height threshold, there are still some options.

We’ve tested child car seats suitable for children up to 150cm/4ft 9in.

They include:

• Cybex Solution G i-Fix
• Joie i-Traver
• Britax Romer Kidfix M i-Size

For more information on choosing a car seat that fits your child, check out our guide to car seat weight groups and height groups.

What are the rules for booster seats or cushions?

It's legal to use booster seats or booster cushions as car seats for children, but the rules differ depending on whether the seats are old or new. 

Since 1 March 2017, backless booster seats can only be used with children taller than 125cm and weighing more than 22kg.

However, backless booster seats made before this date are still legal and approved for use by children weighing 15-36kg (although we wouldn't recommend this).

Shops can also sell backless booster seats that are approved for use by children weighing between 15kg and 36kg, so you’ll need to check the label before you buy to make sure the booster seat corresponds with the size of your child. 

Make sure you're fully clued up with our comprehensive guide to car seat laws in the UK

Should a child be in a backless booster seat?

Our car seat experts believe backless cushions are not the best way to transport children and we recommend using a high-back booster seat whenever possible.

In our rigorous crash tests, backless booster seats haven’t proved to be nearly as safe as high-back booster seats with a full-length back and wings, which provide extra protection for your child's head and chest in a side-impact crash.

In February 2022 we surveyed 2,004 parents who have at least one child under five. A worrying proportion (25%) believe that a backless booster seat offers the same protection as a high-back booster – but this isn't the case. 

Booster cushions raise the child’s position, but some struggle to keep the shoulder strap of a three-point adult seatbelt in the right place on a child, and provide virtually no protection from a side-on collision.

Some manufacturers of backless boosters argue that many modern cars have side airbags or other safety features, which should help to protect the occupants. 

But our child car seat experts disagree, as not every car has added safety features. There’s also a risk that a young child sitting on a booster cushion could easily wriggle out of position – we’ve seen this happen in our fitting tests. What’s more, a young child might not be tall enough for their head to reach the side airbags.

We’ve tested a handful of multi-group seats that convert to a backless booster seat in Group 3 mode, and have given them our Don't Buy warning because of their poor crash-test results, especially for side-impact crashes. A good result in any other part of our crash tests can't compensate for this.

Booster seats are temptingly priced – some start from as little as £10 – and there’s no doubt they’re convenient. But while using any seat is better than using none, booster seats offer very little protection in a crash, particularly if the vehicle is hit from the side.

Booster seats in taxis

If you’re travelling with your child and need to use a backless booster cushion – for example in a taxi, or if you regularly give a child a lift to school – then follow these tips on how to use one.

• Avoid using a backless booster cushion with young children if at all possible, especially those weighing less than 15kg (around three years old). While some seats are approved for use with such light children, our experts don’t think they offer the best protection.
• Use the booster cushion in the middle back seat of a vehicle if you can. Many consider this to be the safest position.
• Some experts consider a backless booster cushion with 'horns' a better choice, as the horns help to hold the adult seatbelt in place across your child’s tummy.
• Remember, it's illegal not to use a child car seat – not to mention unsafe.

Best baby or child car seats: take a look at our free advice and if you're a Which? member see the top child car seats that impressed in our rigorous lab tests

Isofix and booster seats

Isofix connectors on a high-back booster seat don’t work in the same way as they do for baby or toddler car seats. The connectors are used mainly to keep the seat stable and securely in place when it’s not in use, so it doesn’t fly forward and hit you if you have to brake suddenly.

It’s the adult seatbelt in a Group 2/3 seat that helps to distribute the force of a crash away from a child’s body. Some seats in this category have Isofit connectors, rather than Isofix. They're similar but are more like soft latches, or hooks that attach to the anchor points in your car.

Find out more about how Isofix on Group 2/3 seats works differently in our guide to Isofix car seats.

Where to buy high-back booster seats

These are some of the most searched-for booster seat retailers at the time of writing. Each retailer sells both high-back and backless boosters.

• Amazon carries a massive range of high-back booster seats from brands such as Maxi Cosi, Cybex and Apramo. If you have a Prime subscription, you can order some seats for next-day delivery.
• Argos stocks seats from brands such as Cybex, Britax, and Joie and Maxi Cosi. They offer free in-store click-and-collect, with some boosters available for same-day collection.
• Halfords sells high-back booster seats from Cybex, Graco, Joie, plus several own-brand options. Standard delivery is free for all orders over £15. 
• Smyths has a mix of i-Size child and group 2/3 car seats available with prices starting from £17. Delivery is free on orders over £20 or costs £2.99 for orders between £10 and £20. Brands include Graco, Joie and Cybex. 
• Mamas & Papas stocks a small collection of junior seats. Prices start at around £50 and brands include Joie and Maxi Cosi. Standard and next-day delivery is free on orders over £50.

See which retailers are rated highly by Which? members in our guide to the best and worst baby and child shops