"We know the first two years are a crucial developmental period, but at this point we don't have a clue about the impact of all this media," Ms. Rideout said. "The Nielsen ratings don't even count kids under 2, so there's no commercial ratings available. We're hoping this study provides some base-line data."

The Kaiser study was based on a nationally representative telephone survey conducted last spring among 1,065 parents with children 6 months to 6 years old. The study, whose margin of sampling error was plus or minus three percentage points, found that more than a third of all such children had a television in their bedroom and that those who did spent more time watching than those who did not.

According to the parents' own reports, more than a third live in homes where the television is on almost all the time, even if no one is watching. And children in such homes are much less likely than others to be able to read at ages 4 to 6, though the authors emphasized that the relationship was not necessarily causal.

But it is among the babies and toddlers that the most startling picture emerges. "We've got a mom in the office whose 2-year-old daughter has a special computer table, and she's got her games and her activities and her bookmarked Web sites," Ms. Rideout said. "It's a new phenomenon to have little kids spend this kind of time with the media, and while we don't know what it does, I think there are some red flags."

...."I think the academy was trying to help parents understand that in the very early years of life, what babies and toddlers need most is adults," said Matthew Melmed, executive director of Zero to Three, a national center for infants, toddlers and families. "We're programmed, as human beings, to learn through interpersonal relationships."

Many parents say that they understand that large doses of television are not good for babies and toddlers, and that when these children do watch, it is better to watch with them. But as a real-world matter, parents say, the only time they put the DVD in is when they need a respite from child care.