No child should be allowed more than two hours "screen time" per day and children under the age of two shouldn't be allowed any "screen time" at all, according to a recommendation by the American Academy of Paediatrics. This set me to thinking about how I could possibly set such limitations in my own home, an impossible task when you consider that "screen time" is defined as TV, videos, computer games, Nintendo, PlayStation and GameBoy.

The average child watches six hours of television per day - plus all the other screen activities. My nine-year-old daughter will happily spend two hours "screen time" on GameBoy alone, then sit down to watch four episodes of Sabrina back-to-back.

As for making the "screen" off limits to children under two, how are you going to do that when older siblings have the TV on in the playroom for hours at a time? But before, like me, you are tempted to throw your hands in the air and surrender, consider the reason why the AAP made the recommendation. Research has shown that children who spend more than two hours per day in front of a screen of some description are more prone to depression.

And it's not the depression that causes them to become introverted and turn to the screen. It's actually the screen that causes the depression. Normal, happy children become depressed when they spend too much time on computer games, especially, but also by watching too much TV.

The causes of depression are thought to be two-fold in child screen addicts: first, there is the isolation of dealing with a machine, rather than people. Second, there is the false sense of control which the screen world instills, a control which is absent in the real world.

These points were driven home to me by Dr Daniel Broughton, a paediatrician at the Mayo Clinic in the US and a member of the APP, when he was in Dublin recently to talk to key opinion-formers about the effects of the media on children. He had just seen a computer game where the childplayer was put into attack mode against an attractive, sexy woman and given the choice to rape her or kill her.

"Computer games are introducing children to violence and sexism in way that tells children that violence and sexual exploitation are not really harmful or painful," says Broughton. "There is tremendous concern that this is going to change the way kids may interact with the world." At Columbine High School, kids were killing kids - and violent computer games are thought by some observers to have been a major factor.

Violent computer games are becoming substitutes for social interaction with many children. Moreover, the games have been proven in successive research studies to make children dramatically more aggressive. And the games do not have to be especially violent to do this, though the games industry's ethos would seem to be "the more violence the better".

One new PC game launched for Christmas 2000 is Hooligans - Storm over Europe, in which the player controls the most notorious group of hooligans in Europe. The player must bolster his troops with rewards of drugs, alcohol and violence in order to encourage them to maim, kill and destroy opposing hooligan gangs.

Another big game for Christmas is a morbid and ultraviolent version of Alice in Wonderland, in which Alice is armed and dangerous. And in the kung-fu game, Oni, characters go around killing each other, basically. The heroine leaps up, wraps her legs around her opponent, then spins around and breaks his neck.

The darker and more violent games tend to be full of images of partially clad, bigbreasted women who the player must dominate - this even extends to advertising for computer equipment. One ad for accessories has a young woman in a black bikini with her legs spread wide, with strings attached to her ankles and wrists, inviting the viewer to "be a control freak!". Another ad for accessories, also adorned with a leggy blonde, exhorts the viewer to "hear feel see the evil".

The imagery can be very dark indeed. Quake III relies on "ultra violence", Nazi imagery and demonic symbolism for the majority of its gaming content, which takes the player inside the Third Reich. Two other gory new games, Rune and Severance: Blade of Darkness, focus on the hacking up of bodies. In Severance, you can chop off someone's arm and senselessly beat them into submission with it.

Can this be good for our sons?

With male suicides on the increase, the link between depression and violence and screen time should concern us. And with violence and sex crimes also rising, we need to be cognisant, too, of how TV and PC games are teaching our sons to relate to females. Remember that most sex crimes against children are committed by teenagers against younger children, not to mention teenage boys killing other teenage boys outside discos and on the streets.

Maybe it's time for more parents to have the courage to unplug.