Once your child outgrows a forward-facing child safety seat, they are not quite grown enough to properly fit in a safety belt, and should use a belt-positioning booster seat until they are at least 4’9″ and between 8 and 12 years old.
Children at this stage are not yet ready for adult safety belts, which are designed for 165-pound male adults. A belt which does not fit properly can ride up on your child’s stomach and cause internal organ damage or neck/head injuries.
Booster seats are “pre-crash positioners” that help raise your child up to position the lap portion of the safety belt across your child’s hips/upper thighs and the shoulder belt low across your child’s chest and collarbone allowing for proper protection. In fact, studies show that using a booster seat can reduce risk of injury in a crash by 45 percent over a seat belt alone.
Don’t rush! Each time you “graduate” your child to the next seat, there’s a reduction in the level of protection for your child, so keep your child in each stage for as long as possible.
Also, remember that the safest place for all children under age 13 is in in the back seat.