Because children's lives increasingly revolve around video screens and fast food, it's no wonder that many kids—like their parents—are overweight. But pediatric health experts now warn that childhood obesity has become an urgent national problem. A survey published in the Archives of Pediatrics & Adolescent Medicine in 1995 reported that one out of every eight American kids suffers from obesity and that another one in five is overweight. Among those under age 17, obesity has more than doubled in the U.S. since the mid-1960s. According to a recent study led by Dr. Richard Strauss, director of the childhood-weight-control program at the Robert Wood Johnson Medical School in New Brunswick, N.J., the changes in young people's diets and especially physical activity are even more dramatic than commonly thought. "It's a myth that kids today are active and full of energy," says Strauss, 37. "On average the children we studied spent only 12 minutes a day running or playing hard." He talked recently with correspondent Sue Miller.

How do you define obesity in children?

Typically children who are about 25 lbs. above their ideal body weight are considered overweight, and those 40 to 50 lbs. above their ideal body weight are considered obese. But this may vary depending on an individual child's age, sex and body build. Your family doctor should be able to determine fairly quickly if your child has a serious weight problem.

What did your study find?

Our chief finding was that kids are even more sedentary than most people would imagine. We equipped a group of 100 children with beeper-size motion detectors and found that three-quarters of their waking day the kids were barely moving at all. When they did move, it was mostly low-level activity such as slow walking.

How do you explain it?

Twenty years ago children would play outside on the street until it got dark, and there were maybe five channels on TV. Being indoors was boring. Now you have 60 to 100 channels, plus computers and video games. And parents, who tend to work longer hours, often prefer that kids stay home for safety reasons.

How have eating habits changed?

A third of meals are now eaten outside the home, and those tend to be high-fat, big portions. Soda consumption has increased from approximately 19 gallons per person per year in 1965 to over 52 gallons in 1994—a 174 percent increase. And remember: Even small increases in calorie intake or changes in exercise can add up. A difference of 50 calories a day in eating, activity or metabolism adds up to over 15,000 calories, or 5 lbs., a year.

How big is the problem?

Obesity and physical inactivity account for approximately $100 billion in health care expenditures each year. Hypertension, high cholesterol, diabetes, orthopedic problems and severe sleep apnea can occur in very overweight children. But the most significant medical issues are social and emotional. Obesity affects self-esteem.

Is it usually hereditary?

In previous generations there is strong evidence that heredity was the most important determinant of body weight. But genetics can't explain why child obesity has doubled in the last 30 years. It's our way of life that has changed.

Is this just a U.S. problem?

Not at all. We see this trend in every developed and developing country. In China childhood obesity is increasing at a rate of about 10 percent a year. Obesity has increased 10 to 40 percent in the majority of European countries in the last 10 years. It's happening for the same reasons: Families are spending less time being physically active and are adopting a high-fat, low-fiber diet.

How do you treat obese children?

The main methods are improved eating habits and increased activity. Setting a realistic goal is extremely important. Highly restrictive diets are not appropriate for the majority of children, but healthier eating is. Older children often benefit from keeping food records. It's impossible to change those habits if you don't know what you're eating or why. Many people eat out of boredom, loneliness or stress. For those who are seriously overweight with medical complications, we occasionally advise a restricted diet under medical supervision.

What should parents do?

Childhood obesity is a family issue, and we shouldn't just target the child. Improving the eating habits and activity levels of the entire family is necessary. Limiting TV viewing, video games and computer time is essential. Physical activity is also important. I truly believe that unless a child learns to enjoy vegetables, fruits, whole-grain foods and physical activity, little can be done.