Children younger than 12 are at heightened risk of suffering a spinal injury during a car accident — possibly because standard seat belts often do not fit them properly, researchers report.

In a study of children treated for car accident injuries at two Australian hospitals, researchers found that those younger than 12 were seven times more likely than their older counterparts to sustain a serious spine injury. [abs]

All of the 72 children and teenagers in the study had been restrained at the time of the accident. The higher spine-injury risk before age 12 "may reflect the adequacy of seat belt fit," the researchers report in the Archives of Disease in Childhood.

Because standard adult seat belts do not fit smaller children properly, experts advise parents to use car booster seats for children who have outgrown traditional child safety seats.

"However, in most countries the uppermost design mass of boosters effectively limits booster seat use to children up to the age of approximately 8 years," write Drs. Julie Brown and Lynne E. Bilston of the University of New South Wales in Sydney.

These findings suggest there is room for improving seat belt fit for older children, Brown told Reuters Health.

And that, she explained, means modifications to both seat belts and the seats themselves.

Studies show that most rear-seat passengers are younger than 18. But Brown said that rear-seat cushions are too long for many children, even older ones — which causes them to "slouch" in order to bend their knees over the front of the seat.

That, in turn, can upset the proper positioning of their seat belts. The shoulder strap, Brown noted, should pass over the shoulder and center of the chest, while the lap belt should cross low, over the hip bones.

"Vehicle manufacturers need to design the rear seats of their vehicles so that this is achieved and maintained during a crash," Brown said.

For now, she advised parents to use car booster seats for as long as possible — until they are about 4 feet, 9 inches and can sit comfortably with their knees over the front of the seat, without slouching.

Some older kids may be relatively short but too large for most booster seats. Brown noted that some seats are designed with different shapes that may be a better fit for older children.