They have warned that youngsters, especially boys, are at risk from watching unsupervised TV programmes, video movies and games that have violent scenes.

"The availability of video film, satellite and cable TV in the home allows children to access violent media inappropriate to their age, development stage and mental health," the researchers have written in next Saturday's issue of The Lancet.

"Parents and caregivers might be recommended to exercise the same care with adult media entertainment as they do with medication and chemicals around the home," they warned.

"Carelessness with material that contains extreme violent and sexual imagery might even be regarded as a form of emotional child maltreatment."

Reviewing research

The article, written by University of Birmingham psychologists Kevin Browne and Catherine Hamilton-Giachritsis, looked at six "meta-analyses" - overviews of research - on the effects of media violence on children.

"The availability of video film, satellite and cable TV in the home allows children to access violent media inappropriate to their age, development stage and mental health"

Kevin Browne and Catherine Hamilton-Giachritsis,
University of Birmingham

These studies, all of them from North America, comprised two that focused on the effects of violence in TV and films, and four that focused on violence in video and computer games.

From this work, the British duo concluded that violent imagery clearly has "short-term effects" by arousing emotions in younger children "increasing the likelihood of aggressive or fearful behaviour".

Grey areas

The short-term effects on older children and teenagers, as well as the impact in the long-term, are unclear, mainly because so little quality research has been carried out.

There is only "weak evidence" from studies that a child who has been watching screen violence will be directly motivated to commit a crime, says Browne and Hamilton-Giachritsis, cautioning, however, that this too was a largely unexplored area.

The authors admit that the picture is complex, noting that there is evidence that family and social influence can amplify the effects of exposure to violent imagery.

For instance, a child who has grown up in a violent family is likely to become more aggressive after watching film violence than a child who has grown up in households where there is no violence.