Choosing a car seat for your growing baby

Car seats

Once your baby has outgrown their baby car seat, you'll need to buy a bigger one. Just as with car seats for newborns, there are some important things to consider when you're buying a new car seat. If you need information on car seats for your newborn please see our car seats guide for your newborn baby.

Know the law about car seats

As the driver you are legally responsible for using an appropriate child car seat for children up to 135cm (4ft 5in). Safety experts go even further and recommend using a car seat for children up to 150cm (4ft 11in).

You need to check that:

  • Your car seat conforms to the United Nations standard, ECE Regulation 44/03 or ECE 44/04 (look for this on a label on the seat)
  • The car seat is the correct type (known as 'group') for the weight of your child. Weight is more important than age when choosing the right car seat
  • Your car seat is correctly fitted in your car. Follow the car seat manufacturer's instructions carefully when securing your seat.

For more details on the law for using car seats, including rare exceptions, please visit the Which? site.

Choose a car seat for your growing baby and toddler

When the time comes to change your newborn baby car seat for a larger one, there are three groups to choose from (depending on which baby seat you originally bought).

All of these are forward facing but remember that keeping your child in a rear-facing car seat until they are 13kg (29lb) is considered safest.

Buying a combined group car seat (such as 1 and 2) can be a money-saving choice, as it will last your child for longer.

1 9-18kg (20-40lb) 9 months-4 years
1 and 2 9 months-6 years 9 months-4 years
2 15-25kg (33-55lb) 4-6 years

Choose a booster seat for your child

Once your child has outgrown their Group 1 and 2 seat, you'll need to use a booster seat until they're at least 36kg or 135cm tall. This is because they are still too small to benefit from the full protection of an adult seat belt, which should sit comfortably across their collar bone, shoulder and pelvis. Booster seats can be just a backless base to sit on, or a high-backed model, which helps protect your child's head in the case of side impact.

Combination Group 1, 2 and 3 car seats use a 3- or 5-point harness until your child is around four years old. Then, they can be converted into a booster and used with an adult seat belt.

2 15-25kg (33-55lb) 4-6 years
2 and 3 15-36kg (33-79lb) 4-12 years
1, 2 and 3 9-36kg (20-79lb) 9 months-12 years

Fit your car seat correctly

Fitting your car seat safely and securely is crucial. You'll find detailed instructions with the car seat and many seat manufacturers have instruction videos on their websites. Here are a few general tips:


  • practise getting the car seat in and out of your car before your child uses it.
  • check the car seat belt is long enough to secure the child car seat and that it can go through the slits in the car seat without any obstructions.
  • check your car has ISOFIX mounting points if you plan to use an ISOFIX base.
  • adjust the integral harness every time you travel. It should fit snugly, with no more than a finger's space between the harness and your child's chest.
  • checkthe harness straps in a forward-facing car seat are level with, or slightly above, your child's shoulders.
  • check that the car seat has minimal forward or sideways movement. When you open the seat belt buckle, the car seat should spring upwards slightly.
  • make sure the seat belt isn't twisted.


  • allow seat belt buckles to lie against the child seat. Pressure on the buckle during an accident could make it fail. Only the fabric of the seat belt should touch the car seat.
  • use a car seat that makes your child pull up their legs to fit in. If they can't stretch their legs comfortably you have fitted the seat incorrectly, positioned the front seat too far back or bought the wrong group car seat.
  • buy second-hand car seats. Signs of being in an accident aren't always visible.
  • let metal buckles get hot in direct sunlight. Use a window blind to prevent this happening, or cover buckles with a light fabric. Be careful not to let your child overheat.
  • use a cushion or other makeshift support under your child instead of a booster seat. It won't do the same job.
  • allow too much slack. The car seat shouldn't be able to move too far forward or to the side. If it can, check the instructions, move the car seat to another position or consider returning the seat and buying another one.
  • use a lap-only seat belt. Child car seats are designed for use with a three-point diagonal seat belt (or ISOFIX system) and using a lap-only one could cause the seat to flip over in a crash.
  • allow the front seat headrest to touch your child's car seat. If it does, remove the headrest. Don't ever use the headrest to 'jam' the car seat in place. The car seat needs to move forward in a crash to protect your child's head and neck.

Check restraint options

Generally, Group 2 and Group 3 booster seats use your car's normal seat belt to secure both the seat and your child.

If you need information on car seats for your newborn baby please see our car seats guide for your newborn baby.