While all states use some combination of age and weight requirements for children and the mandatory use of child restraints in the form of car seats or booster seats, the overwhelming majority of states have no associated or alternative height requirement, according to the National Highway Traffic Safety Administration (NHTSA). There is, however, a height recommendation advanced by NHTSA, and through billboards and other media, NHTSA is promoting the message that children should ride in booster seats until they are at least 4-feet, 9 inches tall. The reason is very simple – seat belts, according to NHTSA, are designed for people who are at least that tall. In fact, NHTSA also reports that shorter children wearing seat belts only are four times more likely to suffer serious head injuries during a collision than children in child seats or booster seats.
According to NHTSA, a child could safely move out of a booster seat when he can place his back firmly against the vehicle’s seat back with his knees bent over the vehicle seat cushion. The lap belt would have to fit low and tight over his upper thighs, and the shoulder belt should rest over his shoulder and across his chest. NHTSA encourages parents to Know the Facts About Booster Seats and provides useful information in its Child Passenger Safety Program.