Pediatric occupants of motor vehicles need the specialized protection provided by child restraint systems because of their immature and developing body structures. The best child restraint system for a child depends on the size, age, and development level. As children proceed through the four phases of restraints systems (rear-facing harnessed restraints, forward-facing harnessed restraints, belt-positioning booster seats, and seat belts), their level of protection decreases, so graduation to the next type of product should be delayed as long as possible given the specifications for each product. The protection afforded children in crashes also depends on their seating position and safety features in the vehicles. Even when the most appropriate child restraint is selected, its ability to provide protection in a crash depends on how it is installed and used. This review describes how the basic principles of occupant protection are applied to the design of child restraint systems. Best practice recommendations for child occupant protection (primarily from the US perspective) are outlined, together with the research basis that supports them.