The purpose of a booster seat is to provide a proper fit for a child with a seatbelt designed for an adult. By boosting the child, the safety restraint can better protect them in the event of a crash. Proper fit includes a lap belt that fits flat across the child's upper thighs and a shoulder belt that sits in the middle of the shoulder firmly. There are 2 kinds of booster seats: high back and backless. High back boosters can sometimes be converted into backless boosters and are especially recommended in vehicles that do not have head restraints in the back seat. Backless boosters are often more affordable and popular with older children. They may require a plastic clip to properly position the shoulder belt. For additional information on car seat safety you can visit the Children's Hospital of Philadelphia.