Your child should stay in a car safety seat with a full harness until the seat is outgrown, usually at about 40 pounds. When a child's shoulders are above the top set of strap slots, it is time for a booster seat.
Booster seats protect the child's upper body with either the shoulder belt or with a shield. The booster also raises the child so the vehicle lap/shoulder belt fits well.
Why use a booster seat instead of a safety belt?
Most 40-pound children are not big enough to fit lap and shoulder belts properly.A belt that rides up on the tummy could cause serious injury.The adult lap and shoulder belt normally does not fit a child until they are about 4'9" tall and weigh approx. 80 lbs.Many young children do not sit still enough or straight enough to keep lap belts low across their thighs.Boosters are comfortable for children because they allow their legs to bend normally. This also reduces slouching, one cause of poor lap belt fit.
Three kinds of booster seats (A):
1.Boosters without shields, for use only with the vehicle lap/shoulder belt. (left, right) Because raising the child improves belt fit, these are called belt-positioning boosters. Some have a high back that gives head support for taller children. (right) Some boosters of this type are built into vehicle seats.
2.Boosters with removable shields. Use without the shield to make lap and shoulder belts fit right. Shield boosters are not currently approved for children weighing over 40 pounds. A child who has outgrown their convertible seat, yet weighs less than 40 pounds can be moved into a high-back booster with a harness. Once the child reaches 40 pounds, the harness is removed and the seat is used with the adult lap and shoulder belt as a belt-positioning booster.
3. High-backed boosters, used as belt-positioning boosters (right). Most have a clip or strap to hold the shoulder belt in place.
Some high-backed boosters have removable harnesses (B, on back). This type can be used with the harness for a child under 40 lbs.
Children who reach 40 pounds before age 3 may not be mature enough to stay seated properly in a belt-positioning booster. A vest that uses the belt system and a tether strap would be an option in this situation.
Which booster is best?
The belt-positioning booster (B) and (C) is the best choice if your car has combination lap/shoulder belts in the rear seat.Use a booster with a high back if there is no head restraint for the child.The booster with a high back and a removable harness (B) provides the most options in many vehicles. Check the label for the weight limit on the harness.
How long should the booster be used?
Try the vehicle belts on your child as he or she grows taller. When the child sits comfortably without slouching, with the lap belt low on the hips and the shoulder belt across the shoulder, use the belts without the booster. Lap belt fit is most important. A child is usually ready for the adult lap and shoulder belt when the child can sit with their back against the vehicle seat back cushion with knees bent over the vehicle seat edge with feet on the floor.Do your child's ears come above the top of the vehicle seat back? If so, a high-back booster will improve neck protection (B).Always follow manufacturer instructions.
How should a lap belt fit?
The lap belt should fit low over a child's upper thighs (D). Make sure the child sits straight against the seat back. Keep the belt snug. If the lap belt rides up onto the tummy, it could cause serious injuries in a crash.
How can you make a shoulder belt fit better?
The shoulder belt should stay on the shoulder and be close to the childs chest.If you have the kind of shoulder belt that stays loose when it is pulled out, make sure there is no more than one inch of slack. Too much slack will prevent the belt from working well. Teach your child to tug at the shoulder belt to take up excess slack.If the shoulder belt fits so poorly that it goes across the neck or face, raise the child with a belt-positioning booster.
NEVER put a shoulder belt under the child's arm or behind the back. Either of these kinds of misuse could cause serious injury in a crash.Warning: Some devices advertised to improve belt fit for older children and adults are not covered by government standards. They may help with shoulder belt comfort but may put too much slack in the shoulder belt or cause the lap belt to ride up. Boosters are a better solution for children who fit in them.