A US study has found that many young children are too obese to fit into standard car-safety seats.

According to the study, just over 283,000 US children aged between one and six would find it impossible to fit into a child safety seat because of their weight.

Nearly 5 per cent, or 182,000, of these children are three-years-old and weigh more than 40 pounds (18 kg).

The study identified only four types of car seats that these children could use, each of which costs between $240 and $270.

"While we await reductions in the childhood obesity epidemic, it is essential to develop child safety seats that can protect children of all shapes and sizes," said Lara Trifiletti, of Ohio State University in Columbus.

"Motor vehicle crashes pose the single greatest risk to children, accounting for 23 per cent of injury deaths among infants and 30 per cent among preschool-aged children.

Lara Trifiletti, Ohio State University: "While we await reductions in the childhood obesity epidemic, it is essential to develop child safety seats that can protect children of all shapes and sizes."

"Options for maximizing the protection of obese children in automobiles must be identified."

Trifiletti said there was an immediate need for child safety seats that have been designed, tested and approved for use at higher weights.

"Debate regarding what to do to reduce and to prevent childhood obesity is just beginning," she added.

"We do know, however, that childhood obesity is increasing, and we can expect even more children to face the prospect of limited child safety seats available to protect them."

The study is published in the in the April issue of Pediatric.