Why do children need child restraints?
When a vehicle is involved in a crash it comes to an abrupt halt. If unrestrained, occupants will be thrown forwards and have their own crash into the vehicle structure. Restraint systems are therefore designed to help keep people away from the vehicle structure and to distribute the forces of a crash over the strongest parts of the human body, with minimum damage to the soft tissues.
Adults are restrained by a three point seat belt. This is designed for adults and not for children. Children are not small adults. They are proportioned differently and their key organs are in different places. Their tissues have different strengths and weaknesses and their needs change as they grow. Therefore they need a child restraint system to cope with the different stages of their development.