By Cheryl Jensen

Motor Matters

Seat belts are designed to properly restrain adults, not children. They won’t fit children properly until they are around the age of eight or nine, or until they are approximately 4-feet 9-inches tall.

When children no longer fit in a child safety seat, they should graduate to a booster seat, which is a belt-positioning device, not to a seat belt.

Forward facing child safety seats generally fit children until they are 40 pounds or four years old. Children are too tall for child safety seats when their shoulders are above the top strap slots. At that point they can be moved into a booster seat.

Booster seats are not anchored the way child safety seats are; they simply raise the child so that the seat belt fits properly, which means that the lap belt fits low across the hips and the shoulder belt fits across the shoulder and chest.

“This way the forces of the crash are spread over hard bones instead of the soft abdomen,” said Dr. Flaura Koplin Winston, director of TraumaLink at the Children’s Hospital of Philadelphia and the University of Pennsylvania.

Some belt-positioning booster seats have high backs and some are backless, just platforms on which a child sits. Others are a combination of child safety seat and booster seat. Which one is appropriate depends on the size of the child, the height of the vehicle’s seatback, and whether it has a head restraint.

If the vehicle’s seatback is tall enough to support the child’s head, a built-in back is not needed, safety researchers say. Backless boosters also have the advantage of not looking like a child safety seat for younger children. Boosters without backs are the least expensive, generally under $30.

If a child is sitting on a backless booster, and his or her head sticks up above the seatback, and there are no head restraints, then a high-back booster is needed to support that child’s head and prevent whiplash in a crash.

Some booster seats with backs have built-in harnesses. These are sometimes called “combination seats” or “toddler/boosters.” They are appropriate for children who are tall and don’t yet weigh 40 pounds. They first are used with the harness as regular child safety seats by children up to 40 pounds. Later, the internal harness can be removed and the seat can be used as a booster.

Safety researchers generally agree that booster seats can help protect children in a crash. Booster seats are sold wherever child safety seats are sold. But what should a parent look for when buying booster seats?

Simply walking into a store and buying a booster seat does not necessarily guarantee that the vehicle’s lap and shoulder belt will fit a child better, according to a study by the Insurance Institute for Highway Safety. If they make the seat belts fit worse, serious injuries to internal organs such as the liver, spleen and stomach could occur.

The goal is for the lap belt to be as low as possible across the hips, touching the tops of the thighs, safety researchers say. The shoulder belt should come across the middle of the chest. It should also pass flatly across the shoulder about halfway between the neck and arm.

Another important factor involves the guides through which the car’s shoulder belts are routed in high-back boosters. These are designed to properly position the shoulder belt, but Consumer Reports’ testing found that some of the guides could cause the seat belt to bind.

This binding could endanger children when they move forward and loosen the shoulder belt, which then might not fully retract. That would leave slack, which means the belt might not fully restrain a child in a crash.

Consumer Reports recommends an open loop with enough room on each side of the belt so that it can move freely and not bind.

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