A poll, conducted by the Royal Children's Hospital, found 63 per cent of children aged seven to 10 travel with an adult seat belt without a booster seat, despite many being below the recommended safety height.
Only three per cent of parents surveyed knew their child needs to be at least 145cm tall to safely travel with just an adult seatbelt.
"This study shows that parents are unaware of best practice recommendations when it comes to car seats and kids," RCH National Child Health Poll Director, Dr Anthea Rhodes, said.
Parents are following the law, but unfortunately the law does not reflect safest practice, and this means many parents are unknowingly putting their children at risk of serious injury or death every day."
Rhodes said a review of the country's laws around child car restraints is needed.
She says it is critical for parents to measure their children before transitioning them out of a booster seat.
And most kids do not reach 145cm tall until they are about 11 years of age.
The nationwide poll surveyed 1,639 parents caring for 2,778 children aged from one month to 13 years.
It found the most common age for children first travelling without a booster seat is seven.
Half of children aged between seven and 12 also travel in the front seat of the car, and two thirds are in forward-facing car seats by 18 months of age - despite recommendations that rear-facing is safer until they reach two, according to the poll.
This article first appeared on 7News.