A Lincolnshire road safety group says more than half of parents in the county are not asking their children to wear seat belts.
The Lincolnshire Road Safety Partnership says its studies over two years show that 60% of children do not put on their seat belts.
It is urging parents to make sure everyone wears a seat belt in the car - even on the shortest journey.
The group also says women are the most likely to ignore the law.
The figures show that 65% of drivers caught not wearing seat belts were women.
Six fatal accidents in 2004 - four involving women - could have been prevented had the driver worn a seat belt, the safety group says.