"Arthur" and "Barney" are OK for toddler TV-watching. But not "Rugrats" and certainly not "Power Rangers," reports a new study of early TV-watching and future attention problems.

The research involved children younger than 3, so TV is mostly a no-no anyway, according to the experts. But if TV is allowed, it should be of the educational variety, the researchers said.

Every hour per day that kids under 3 watched violent child-oriented entertainment their risk doubled for attention problems five years later, the study found. Even nonviolent kids' shows like "Rugrats" and "The Flintstones" carried a still substantial risk for attention problems, though slightly lower.

On the other hand, educational shows, including "Arthur," "Barney" and "Sesame Street" had no association with future attention problems.

Interestingly, the risks only occurred in children younger than age 3, perhaps because that is a particularly crucial period of brain development. Those results echo a different study last month that suggested TV watching has less impact on older children's behavior than on toddlers.

The American Academy of Pediatrics recommends no television for children younger than 2 and limited TV for older children.

The current study by University of Washington researchers was prepared for release Monday in November's issue of the journal Pediatrics.

Previous research and news reports on TV's effects have tended to view television as a single entity, without regard to content. But "the reality is that it's not inherently good or bad. It really depends on what they watch," said Dr. Dimitri Christakis, who co-authored the study with researcher Frederick Zimmerman.

Their study was based on parent questionnaires. They acknowledge it's observational data that only suggests a link and isn't proof that TV habits cause attention problems. Still, they think the connection is plausible.

The researchers called a show violent if it involved fighting, hitting people, threats or other violence that were central to the plot or a main character. Shows listed included "Power Rangers," "Lion King" and "Scooby Doo."