Car seats for older children: high-back vs backless booster seats - Which? (2022)

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.

For older children (from around the age of four), this usually takes the form of a either a high-back or backless booster seat. But what's the difference between the two?

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

What is a high-back booster seat?

Your child's bones continue to strengthen as they grow older, and once they reach around 18kg (usually around four years old), or they are taller than 105cm, you can swap to a high-back booster seat (Group 2/3 or i-Size).

Group 2/3 child car seats are approved for use with children from 15kg to 36kg, which is around three and a half to 12 years of age (around 36kg). If it's an i-size R129 seat, they're usually suitable for children measuring 100 to 150cm.

There's no need to swap to this next size up of seat until your child has outgrown his or her toddler seat.

These car seats raise the position of your child and help guide the adult seat belt across them, so that it lies properly across the chest and pelvis. They also have a protective headrest and side wings, which will help protect your child's head in a crash.

What is a backless booster seat?

Booster seats are backless cushions that you can use as a child car seat. Under R44.04 regulations, they're known as Group 3 seats.

A booster seat can help to raise a child's body to a height suitable for using the adult seatbelt. Some have ‘horns’ that help the car’s adult seatbelt to sit across your child’s tummy.

You can buy booster seats that are simply the cushion part. But some Group 2/3 car seats also convert to a booster cushion for Group 3 mode. Essentially, this removes the seat's protective sides (Group 2) and turns the seat into a booster cushion.

Booster seats are temptingly cheap – some start from as little as £6 – 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.

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 they're old or new.

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

However, backless booster seats made and bought before this date are still legal and approved for use by children weighing between 15kg and 36kg. So, if you own a backless booster seat bought before this date, you can still use it for a child within this weight range (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.

Find out more about car seat law in the UK

Car seats for older children: high-back vs backless booster seats - Which? (1)

Should a child be in a backless booster seat?

Our car seat experts and many others believe these backless cushions are not the best way to transport children. It is recommended to use a high-back booster seat instead, whenever possible.

The booster seats we've tested have not proved as safe in our crash tests as high-back booster seats with a full-length back and 'wings', as these provide extra protection for the head and chest in a side-impact crash.

Find those that came top in our crash tests in our car seat reviews

In February 2022 we surveyed 2,004 parents who have at least one child under five. A worrying number of parents (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 position of the child, but some struggle with keeping the shoulder strap of a three-point adult seatbelt in the right place on a child, and provide virtually no side-impact protection if you’re involved in 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.

Car seats for older children: high-back vs backless booster seats - Which? (2)

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 these are Don't Buys 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.

Some booster cushions do so badly in our crash tests that the results meant the score was instantly downgraded to a 0% Don't Buy – our lowest possible score.

Booster seats in taxis

Car seats for older children: high-back vs backless booster seats - Which? (3)

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 read on for tips below 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 in a vehicle.
  • Some experts consider a backless booster cushion with 'horns' a better choice, as the horns help 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.

MiFold Grab and Go review – is it safe? Read our review and find out before you splash out.

Isofix and booster seats

Car seats for older children: high-back vs backless booster seats - Which? (4)

Isofix connectors on a high-backed 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 or are involved in a crash and the kids aren't on board.

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 in our Isofix car seats guide.

What are the best child car seats for tall children?

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

We’ve tested child car seats that can be used up to 150cm/4ft 9in.

They include:

  • Nuna Myti review
  • Britax Romer KidFix2 S review
  • BeSafe Izi Flex Fix i-Size review

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