At home, the phrase "Go watch TV" to kids has replaced "Go outside and play" in many families. At school, the daily hour of recess is dwindling. The combination is contributing to many kids not getting enough exercise, according to some experts.
"Parents are not allowing their kids to play after school because of the safety issue and all of the child abuse issues we've seen over the last 15 to 20 years," said Steve Virgilio, a physical education professor at Adelphi University in New York. "Parents are happy to have children in front of the TV or DVD or the computer because they know they're safe."
But throw in an almost daily dose of junk food and you've got a recipe for childhood obesity.
A 2003-2004 survey by the Centers for Disease Control and Prevention found that about 17 percent of children between the ages of 2 and 19 were overweight.
Compare that with figures from just a generation ago: Federal data from the late 1970s showed that 7 percent of 6- to 11-year-olds and just 5 percent of 12- to 19-year-olds were overweight.
"Children are inherently physically active, but it's up to the adult population, whether it's caregivers at preschools or teachers or parents or grandparents, to make sure that they understand that physical activity is a big part of their life," Virgilio said.
A newly released study conducted by the U.S. Department of Education found that 99 percent of public elementary schools had some scheduled physical education in 2005. But how often activity is scheduled varies. Between 17 and 22 percent of students had P.E. every day; about half had one or two days each week.
The average amount of time spent at recess and physical education was about 221 minutes per week for first-graders and 214 minutes for sixth-graders.
And participation in gym class drops steadily in high school, according to the CDC. In 2003, almost 38 percent of freshmen had daily P.E. classes, but that number dropped to about 18 percent for seniors.
Sixty-eight percent of freshmen said they exercised hard enough to sweat and breathe hard in at least three of the past seven days compared to 55 percent of seniors. But more than 9 percent of freshmen and 12 percent of seniors said they had participated in no vigorous or moderate activity during that period, the CDC found.
Bill Modzeleski, who heads the U.S. Department of Education's safe and drug-free schools department, said the agency is working with schools to help children develop life-long habits.
"This is about educating kids about healthy eating and healthy habits as well as just physical fitness," he said. "We're talking about getting kids at a very early age to understand that exercise is not only important, but it can be fun."
Virgilio said that preschoolers need at least an hour and a half of activity each day.
"One of the guidelines is that children should not be sedentary for more than 60 minutes at a time. In other words, after 60 minutes they should be up and moving for 10 minutes blocks of time," he said. "As children move into elementary school, they shouldn't be sedentary for more than 90 minutes at a time."
But that doesn't mean that they have to be running, or hitting the gym -- anything that gets their big muscles involved will work.
Even an old shoe and a piece of rope can be turned into a fun fitness tool in a pinch.
"You tie a shoe to the end of a piece of rope and then you just twirl it around and the children try to jump over the shoe," Virgilio said. "That's something that you can do for 10 minutes that children can have fun with.
Even marching around the room for five minutes, pretending to be in a band is fine, he said.
"They don't have to go out and run, they don't need to get down and do sit-ups and push-ups and so on -- they just need good physical activity."