Too Much Fat and TV in U.S. Children’s Lives, Report Says : Health: A magazine survey also finds that parents seem to be aiding youngsters’ bad habits.

American children still eat too much fat and sugar and, instead of working off the calories, watch enough TV to steal two months out of each year, a health survey says.

Prevention magazine says two-thirds of U.S. children fail its Children’s Health Index, a measure of good health and safety released Tuesday.

Its most surprising finding was that parents appear to be slacking off in the nutrition battle even as their kids get fatter.

About 31% of children ages 3 to 17 are overweight, an increase of 29% since 1984, the survey said.

But only 50% of parents surveyed try to limit fat in their menus, down from 64% in 1991. Only 49% fight sugar, down from 72%. Competing information on what’s best to eat might be overwhelming parents, Prevention’s Tom Dybdahl said. “Lots of people are feeling, ‘I might just as well eat what I want.’ ”

But children also spend 912 hours a year watching television--equal to two months of waking hours, the survey said.

Yet parents report that 66% of children get 20 minutes of strenuous exercise at least three times a week.

“Clearly, parents need to be educated about the difference between an active child, which is normal, and one who is physically fit,” said Prevention managing editor Lewis Vaughn.

Among the survey’s other findings:

* 41% of the families that own guns say the weapons are “just hidden away” and not locked up.

* Only one-third of all children and 13% of teen-agers wear helmets while bicycling.

The Health Index is based on a telephone survey of 424 parents by Princeton Survey Research Associates. It has an error margin of plus or minus 5 percentage points.