Children under two should not be allowed to watch any TV, experts say.
Some children watch too much TV
Older children should watch no more than two hours a day, the researchers at the Children's Hospital and Regional Medical Centre in Seattle said.
Each hour in front of the TV increased a child's chances of attention deficit disorder by 10%, their research in the Pediatrics journal showed.
The study of 1,345 children showed three hours TV a day made children 30% more likely to have the disorder.
Dr Dimitri Christakis at the children's hospital led the study. He said: "The newborn brain develops very rapidly during the first two to three years of life. It's really being wired."
Children who were exposed to the unrealistic levels of stimulation at a young age continued to expect this in later life, leading to difficulty dealing with the slower pace of school and homework, he said.
"TV can cause the developing mind to experience unnatural levels of stimulation," he said.
This was made worse by the rapid image change that television makers used to keep young children interested, Dr Christakis added.
Parents were questioned about their children's viewing habits and asked to rate their behaviour at age seven on a scale similar to that used to diagnose attention deficit disorders.
The youngsters who watched the most television were more likely to rank within the top 10% for concentration problems, impulsiveness, restlessness and being
Frederick Zimmerman of the University of Washington in
Seattle, another of the authors, said it was impossible to say what a "safe" level of TV viewing would be for children between the ages of one and three.
"Each hour has an additional risk. You might say there's no safe level since there's a small but increased risk with each hour," he said.
"Things are a trade-off. Some parents might want to take that risk. We didn't find a safe level in that sense."
Between three and five per cent of children in the US are diagnosed with attention deficit disorder.
The researchers admitted there could be problems in the study as the parents' views may not be totally accurate.
Also it was not possible to know whether the children already had attention problems early on that attracted them to TV viewing.