Violent computer games are having a damaging effect on children of primary school age, teachers have warned.
Some are staying up beyond midnight playing games in their bedrooms unsupervised by parents, according to the Association of Teachers and Lecturers (ATL).
The union will debate a motion at its conference next week calling on ministers to investigate the possible introduction of new legal curbs to protect young children from the harmful effects of computer games.
"I think that what we are talking about, first of all, is the amount of time children spend locked in their room," said Mary Bousted, the general secretary of the ATL.
"It means they are not interacting [with other children], they are not playing and they are not taking exercise."
Dr Bousted added that some of the games were very violent and were having an effect on the "tender young minds of children and young people".
"If you've got a game in the house, it's very difficult to police who's playing it," she said.