Half of all family blockbuster films set a bad example to children as characters routinely break basic safety rules, an academic report claims.

Researchers found that the main protagonists of Hollywood movies often undermine accident prevention advice given to children.

Half the scenes examined in movies aimed at children showed unsafe practices including not wearing seat belts, breaking the green cross code and failing to wear helmets on bikes.

The mistakes could give children a "false sense of safety" they claim which could lead to bad habits and encourage dangerous activity.

Dr Jon Eric Tongren, the lead researcher at America's Center for Disease Control and Prevention, said the industry was improving but had a long way to go.

"The entertainment industry has improved the depiction of selected safety practices and PG-rated movies," he said.

"However, approximately one half of scenes depict unsafe practices and the consequences of these behaviours are rarely shown."

Dr Tongren said that it was not a trivial matter as unintentional injuries are the leading cause of death among children, accounting for almost a third of all fatalities affecting children aged one to 14.

Many of these injuries could be prevented with the right safety advice.

Dr Tongren picked out two examples to highlight the problem.

In the 2003 Christmas movie Elf, the main character played by actor Will Ferrell gets knocked down by a New York City taxi while crossing the street.

He bounces back up without a scratch – which Dr Tongren said gave a false view of what happens.

And in the 2005 comedy "Yours, Mine and Ours," about a family with 18 kids, the children are wearing life jackets during a boat trip — but not the parents played by Dennis Quaid and Rene Russo.

The two films were among 67 popular movies from 2003 to 2007 examined in the study including Harry Potter.

Five of the movies were rated G for general release, and the remaining 62 were PG-rated. Thirty-eight movies were comedies, 15 were action/adventure movies, 13 were children/family films and one was a drama

From those movies, the researchers found 958 scenes involving potential injury-prevention practices. Fifty-five per cent of the scenes involved children.

Twenty-two scenes involved either a fall or a crash, but just three of those scenes resulted in an injury

The study, published in the journal, Paediatrics, found 44 per cent of people in motor vehicles failed to wear seat belts; 65 per cent of pedestrians did not cross at zebra crossings, 75 per cent of cyclists failed to wear a helmet and 25 per cent of boaters failed to wear life vests.