In the UK, the law requires all children travelling in vehicles to use the correct child restraint until they are either 135cm in height, or aged 12. After this, they must use an adult seat belt.
The law also states that rear-facing baby seats MUST NOT be used in a seat protected by a frontal airbag, unless the airbag has been deactivated manually or automatically. In addition, all car seats MUST conform to the latest European standard ECE R44.03, or R44.04.
Because it is the driver's legal responsibility to ensure that the child is correctly restrained, choosing the right car-seat - and making sure it fits correctly - is important.