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How much TV do your kids watch? If you don’t know, you might want to find out, say experts, since the time children spend in front of a TV or computer screen can have a profound effect on their physical and developmental health.

In a new policy statement on the role of media on obesity, the American Academy of Pediatrics’ (AAP) Council on Communications and Media warns parents that TV watching doesn’t just make children more sedentary, but also influences their eating habits, which in turn has consequences for their health. In other words, it’s not just that TV watching encourages youngsters to be less physically active, but it also exposes them to food advertisements that contribute to develop poor eating habits that can set kids up for health problems as adults.

“We created a perfect storm between media use, junk and fast food advertising, and physical inactivity,” says Dr. Victor Strasburger, professor of pediatrics at the University of New Mexico School of Medicine and member of the AAP’s Council. “We created a situation where we now have more overweight and obese adults in the U.S, than underweight and normal weight adults; it’s become an urgent public health problem.”

The policy statement highlights the fact that the harms of TV viewing go beyond promoting inactivity. More studies have shown that children who spend more time in front of the tube are more likely to eat higher-calorie foods, drink sugared sodas and grow up to be overweight adults. In a U.K. study that followed children over 30 years into adulthood, for every additional hour of TV youngsters watched on weekends at age five, their risk of being obese as adults rose by 7%. And in some cases, it doesn’t even take that long for the extra pounds to accumulate: a Japanese study found that children who watched more TV at age three were more likely to be overweight at age six.

The culprit: advertising for unhealthy foods. (See the video, below.) The average American child sees nearly 8,000 commercials on TV for food and beverages, and only 165 of these are for nutritious options like fruits and vegetables. “Clearly eating behavior changes if you watch a lot of TV,” says Strasburger. “You tend to snack more, eat more unhealthy food and eat more calories if you eat in front of the TV set.”

What can parents do? Limiting TV time to no more than two hours a day can help, says the AAP committee. Another important step toward breaking the TV-obesity link is to make sure that children don’t have TV sets or Internet connections in their bedrooms. Parents should also watch television with their kids, so they can educate them about commercials and learn to distinguish healthy from unhealthy foods.

“Media such as television is the most important and under-appreciated influence on children’s development and behavior,” says Strasburger. “Media affect virtually every concern that parents and pediatricians have about their kids, whether it’s obesity, sex, drugs or school performance. When kids spend up to seven hours a day watching television or on the computer, it’s time to acknowledge that influence and spend money on researching how we can maximize the good effects of media and minimize its bad effects.”

VIDEO: How food companies disguise kid-focused marketing as online games. Watch below: