Child restraint systems provide specialized protection for small occupants whose body structures are still immature and growing. There is a wide variety of systems from which to choose, and different types of restraints are appropriate for children of different ages and sizes. Even with the most appropriate child restraint (CR), however, the way in which it is installed and used can have an effect on its performance. This review describes the theory behind the design of occupant restraint systems and applies these principles to the special needs of children. A distinction is made between child restraints, which themselves provide the restraint structure, and positioning devices, such as boosters, which help the vehicle belt fit the child. Throughout each section, current concepts of best practice are given, including the changes brought on by passenger airbags, and future directions are indicated.