The survey found only one in five car seats was properly fitted

Tests carried out by local authorities across Wales found 80% were not fitted correctly and a third had faults which could not be fixed.

A quarter were unsuitable for the child or incompatible with the car.

Road safety experts will be out across Wales from Monday to advise parents on fitting car seats as part of a Welsh Assembly Government campaign.

Children who are not suitably restrained can be seriously injured or killed in an impact at speeds as low as 5mph Road safety expert Steve Baker

Child car seats are only able to stop children being thrown about inside, or out of, a car involved in a collision - or absorb the impact of a crash - if correctly fitted.

Kimberley Vidal, from Barry, south Wales, said her son Sebastian, now 12, would have been killed in a crash when he was a baby if he had not been in a correctly-fitted car seat.

She said: "If we hadn't had the proper car seat, he would be dead by now.

"They said if we'd had a passenger in there, their legs would have been crushed, the car was just a write-off.

Kimberley Vidal says her son Sebastian was saved by his car seat

"We were really lucky he was in a very good car seat - it did save his life."

According to the research, common mistakes made in fitting included putting adult seat belts in the wrong place or not tightening harnesses and seatbelts enough.

Only a quarter of parents surveyed had been offered advice or a demonstration by the retailer when they bought their car seat.

One in 10 parents was using a second-hand car seat, despite it being strongly discouraged, and nearly three quarters of those had not been supplied with the instructions.

Steve Baker, road safety manager in Wales for the Royal Society for the Prevention of Accidents, said: "When buying a new seat you should take your car with you, check the shop has a trained fitter, and ask to try fitting it before you buy.

"It's important to remember that children who are not suitably restrained can be seriously injured or killed in an impact at speeds as low as 5 mph."