Current UK law states that a child must be in an appropriate restraint until they are 12 years old or 135cm, whichever comes first. Up until this point, their bodies are still developing and they are not big or strong enough to be sufficiently protected without a car seat or booster.
It’s easy to think that when children get to the age of 7 or 8 that they are mature enough to sit in the car like adults but most often they are too small. A seat belt is designed for adults and is specifically installed to sit across their hips and squarely on the shoulder. For younger children who will sit lower, this means the seat belt would go across the abdomen and the neck. Not only is this uncomfortable but in the event of an accident could cause serious injury. Therefore it is important to make sure children are in a booster seat (high back versions offer the most protection) until they reach 12 years or 135cm
There are different categories of car seat. The most common ones which are currently on the market fit into one of the following groups:
Legally these must have a rear facing capacity and most seats accommodate babies up to 13kg. Any new seats which are tested under the new isize regulation will have a rear facing capacity up to 15 months minimum. Rear facing is the safest way to travel because in a frontal collision (the most common) the entire back of the seat supports the child and significantly reduces whiplash type forces on the neck compared with forward facing seats. Group 0/0+ seats can be installed in the car with seatbelts or using the isofix connectors
These can be forward or rear facing but must not accommodate a child forward facing until at least 9kg. They always have a 5 point harness or a shield. Most group 1 seats accommodate a child up to 18kg. Group 1 seats can be installed in the car with seatbelts or using the isofix connectors. Isofix connectors in cars are tested to safely hold up to 33kg. Regulations allow 15kg for the weight of the car seat which means the maximum weight of the child can be 18kg
These seats start off using a 5 point harness but when the child out grows this, it can be removed so the seat is used as a high back booster. Usually they only offer a forward facing position.
This group includes highback and backless boosters, although backless boosters are sometimes referred to as just group 3 seats. Children must be at least 15kg to use a group 2/3 seat although it is recommended to keep them in a 5 point harness for as long as possible.