When can my child start using a car booster seat?

3 children sat on BubbleBum booster seats across the back seat of a car - USA design

In the UK the law states that your child must be seated in an approved children’s car seat  until the age of twelve, or they reach a height of 135cms, whichever comes first.  This is when your child’s proportions begin to closely resemble those of a small adult, meaning that the vehicle seat belt will be more likely to sit in the correct position across their chest and the bony pelvis to provide appropriate protection in the event of a crash.  But when can they start using a booster seat? 

A children’s car booster is a seat belt positioning system, designed to position your child in a way that allows the seat belt to sit across the bony pelvis area, and the chest.  Crucially, this means that the seat belt strap is not falling off the shoulder, or riding upwards towards the soft tissue of the abdomen. When positioned correctly, in the event of a crash, the seat belt will transfer the force to the sturdy structures of the chest and pelvis, reducing the likelihood of debilitating or fatal internal injuries.  However, if the vehicle seat belt is positioned incorrectly, across the abdomen for example, the forces generated during a crash will be transferred from the seatbelt to your child’s delicate vulnerable organs in the abdomen, causing potentially devastating injuries.

Compounding this issue is the fact that your child is not the correct size to be able to sit comfortably in a car seat designed for adults. The length of the base of the vehicle seat, combined with a slight slope towards the seat bight, means that your child’s legs are unable to bend at the knee whilst sitting in an upright position, with their back parallel to the back of the vehicle  seat.  To compensate, and allow their legs to bend into a more comfortable position, children will often slouch forward in their seat.

This is extremely dangerous because it will cause a gap to open up between your child’s hips, and the back of the vehicle seat.  The excess belt length created by this gap slackens the belt, meaning that, in the event of a crash the child is not held securely against the vehicle seat, and is likely to be forced under the seat belt. This series of events has become known as ‘submarining’, and as you can imagine, the injuries caused to your child in this situation can be catastrophic. When used correctly a booster seat removes the tendency to slouch by letting the child’s legs bend in a more natural and comfortable way.



How using a booster seat positions your child’s seat belt to provide optimum protection in the event of a crash.


But when should your child start using a booster seat?

As your child grows, they will begin to look increasingly snug in their 5 point harness (that’s the one with the built in harness).  The bigger they get, the more you might wonder, is it time for them to start using a booster seat yet?

It is advised that children are kept in their 5 point harness seat for as long as possible, which means until they have reached the upper weight limit of the seat (you can find this information in the instruction manual).  When used correctly these seats are the safest way for a child to travel by car, and therefore your children should use them for as long as possible, before transitioning to the next stage.

As you would expect, there are laws surrounding when a child can start using a booster seat; our simple explanation below will help you to know when the time is right.


When can my child start using a booster seat?

When using a booster seat, make sure it has European Certification

Your child can legally start using a car booster seat once they reach 4 years old AND are at least 15 kgs in weight.  It’s important to stress that your child should meet both the age and weight criteria before they can be moved over to a booster seat.

Remember though that transitioning between car seats is not like the milestones from crawling to walking or cutting teeth. Each step forward in children’s car seats is a step down in protection for your child, so it is always safer to keep your child in their infant seat and then their 5 point harness seat until they reach the upper weight limit of that seat.

In the UK, only car seats or booster seats which are in line with EU regulations can be used and this certification will be indicated with a label showing a capital E, along with the code R129 or the code ECE R44.  See the label from a BubbleBum booster seat on the right as an example.

Check out the range of BubbleBum car booster seats here.


In the video below BubbleBum founder and CEO Grainne Kelly demonstrates how to properly secure a child using the BubbleBum booster seat.


A child using a booster seat (BubbleBum Pink Chevron)