We all know by now that too much television is bad for kids - couch potatoes of all ages end up fat. A new report, however, warns that TV can be bad for the brain as well as the body. Toddlers who watch too much can become aggressive and suffer from poor attention span.

The study, carried out in America by Frederick Zimmerman, an associate professor of health services at the University of Washington, is the first to look at media viewing in the first two years of life. It makes for sobering reading.

"Excessive viewing before age three has been shown to be associated with problems of attention control, aggressive behaviour and poor cognitive development," says Zimmerman.

America is the land of extremes, but the report has relevance for Ireland, too. A 2005 report found that one in three small children here has a TV in their room. In some national schools, this figure rises to 60% of all children.

David Egan, director of RedBranch School Health Ltd, a non-profit organisation which aims to improve the health of Irish children, says that primary school students typically watch TV for at least four hours a day.

"That's a sixth of their life," he says. "Often the child will use a computer for a further two hours. And it will have an effect on their behaviour."

Parents, he says, welcome the information on TV this organisation gives. But they find it hard to comply with sensible guidelines.

"They say: 'I cannot possibly take the TV out of the child's bedroom. There will be war.' But that is their job as a parent."

Consulting child psychologist David Coleman, the author of Parenting is Child's Play (Penguin Ireland) and star of RTE's Families in Trouble, welcomes the new report.

"Hopefully it will raise people's awareness of the potential dangers of too much, and unmonitored TV," he says. "It is all about moderation. Parents need to take responsibility for moderating the TV their children watch.

"I've always had the sense that kids who watch too much TV are hyperactive. TV causes, I believe, a mismatch. Children's brains are stimulated, but their bodies are not. As soon as the TV is turned off their brains go into hibernation, and their bodies click into gear. They don't seem able to think and process the information, and they may get physically aggressive."

It's tempting to park a toddler in front of the television now and then, so that we can keep them entertained as we get the housework done, but this isn't such a good idea.

"That does not develop the parent's relationship with the child. TV viewing should be interactive," Coleman says.

Former EastEnders star Michelle Collins recently criticised the BBC for their increasingly violent story lines. The actress, who found fame playing Cindy Beale in the soap, reportedly told BBC's Breakfast News that she watched the omnibus edition and found the programme addressing issues such as abortion.

"There was this really horrible scene," she said. "I thought, 'I don't want to watch this. Not with my 10-year-old daughter, thank you."

Does violence on TV worry Coleman? "Being exposed to violent or sexually explicit material now and then is not necessarily a bad thing; as long as parents can discuss it with them and help them to make sense of it.

"But you have to be aware what they are watching. It can be worrying if children don't get to discuss what they have seen with their parents. They should not be left to process it themselves."

Coleman is also concerned about advertising and small children. "Kids under six do not understand that the main function of advertising is to influence," he says.

"So they watch advertisements and believe they are being told a fact. You have to be aware of what children are watching, and you have to limit their viewing as well."

Patricia Cronnelly and John Punch don't let their children Art (nine), Oscar (five) and Ferdia (11 months) watch any TV at all. They decided as soon as Art was born that it was a time-wasting activity.

"Before we had kids we both worked, and we watched TV sometimes in the evenings," says Patricia. "But the birth of a child makes you very busy.

"The opportunity for conversation is reduced dramatically. So rather than staying up to watch TV we thought, 'Let's stop and just talk.'"

Patricia home schools Art and Oscar. "So if there was a TV in the corner there's be a lot of fighting," she says. "We'd fight over how many hours they could watch.

"Instead of watching TV the boys look at their books, and we read them stories. They play chess, they mess around in the garden on their scooters and things, and we go out for walks in the evenings.

"The boys are always around me, and Art can now cook. He makes pancakes. We always sit down for family meals, and with no TV in the corner we'll be chatting all the time."

Patricia does let the boys older boys watch videos sometimes, and she and John will watch one at the weekend. "That's fine, if the boys have been doing other activities all day," says Patricia.

Isn't there a lot of pressure to let the boys watch TV? "There's more pressure from Art to get play stations and electronic games," says Patricia.

"But I feel those games, like TV, are a terrible waste of time. It's better if the boys are in the woods, the garden or playing in the house. Even fighting is more productive than sitting staring at a screen.

"People say TV can be educational, and that I am depriving the children of pleasure. I think that children want to learn from the people around them. I don't think they should be learning from TV."

TV tot tips

* Do not let your child have a TV in their room.

* Don't have the TV on as background noise.

* Don't allow unsupervised access.

* Agree, in advance, which programmes your child can watch.

* Keep a TV log for a week to see how much you are watching.

* Don't eat in front of the TV.

- Tips from www.redbranch.ie