There are currently two different laws governing child car seats - one based on age and weight of your child, the other based on their height
It's the law to make sure that your child is travelling in the correct car seat for their age and weight or height
Some child car seats are designed to last for several years, so will straddle group definitions
So you've decorated the nursery, stocked up on nappies, got the cot built and bought the cutest outfits. Now for the serious purchase – the car seat.
And it doesn't stop when they're no longer newborn. As your baby grows, you'll need to change the car seat to make sure they're still travelling safely.
It's the law to make sure that your child is travelling in the correct car seat for their age and weight or height.
But over and above that, it's simply unsafe for your child to be in the wrong seat. Children's bodies behave differently in an accident to adult-sized bodies, so need additional support and restraint.
There are currently two different laws governing child car seats. One is based on the age and weight of your child; the other is based on their height.
When you buy a new car seat, or you're replacing a seat because your child has outgrown their current seat, you'll need to buy a seat that conforms to one or other, or both of the regulations.
If your child's seat gets damaged or is involved in an accident, you should buy a replacement straightaway. Your car insurance may cover the cost of the replacement.
Child car seats are split into four groups - Groups 0, 1, 2 and 3 depending on a child's age and weight:
Some child car seats are designed to last for several years so will straddle group definitions. For example, you can buy a car seat that's suitable for a child from the age of 4 to 12.
Which? have put together a how to buy the right child car seat guide that explains the range of seats available.
If you've been doing a bit of internet research into the best car seat for your child you've probably come across the new iSize seat.
All child car seats must conform to certain regulations. 'Group' seats conform to the law that is based on a child's age and weight and iSize seats conform to the law that is based on a child's height.
iSize seats keep your child seated in a rear-facing position until they are 15 months old. Rear-facing seats are considered safer for babies and young toddlers as the relative size of their head to their body puts a huge strain on their neck in a front impact collision.
Both types of seat are safe for your child but the Group system will be phased out over time. At the moment there's no need to replace your existing seat until your child has outgrown it. Which? take a look at how the two systems compare.
Isofix is an easy way to fit a child car seat into your car without using the seatbelt. It uses two metal connectors that are built in to the chassis of the car and hidden by the seats.
The seat is secured by a third anchor point either at the top or bottom of the seat, which stops it tipping forward in an accident.
Isofix is an easy way to fit a child car seat into your car without using the seatbelt.
Don't be tempted to move your child up to a booster seat too soon. Your child can stay in a rear-facing seat until they are 15 months. Then you can move to a Group 1 front-facing seat until they are four years old.
High-backed booster seats are suitable from four years. These seats raise the child up so that the seat belt fits snugly across the lap. The side wings and headrest provide extra protection and help the seatbelt to cross the child's chest in the correct position.
Children should stay in a high-backed booster seat until they are 150cm tall, when they can use a seatbelt without a booster seat.