It's nothing new to see adults tucking their tummies to a videotape. But now kids as young as a year old are doing aerobic workouts with unlikely exercise gurus like Tinky Winky the Teletubbie.

With one in five American children considered overweight and even toddlers becoming chubbier, health experts hope exercise videos aimed at kids will make them more fit than their computer-game playing, TV-watching, couch-potato counterparts.

Some videos have even made it into the classroom. Marilynn Arnold, a physical education teacher at Smith Elementary School in Grandview, Wash., relies on Movin' & Groovin': Fitness for Kids when other classes are using the gym.

"They have a lot of fun. They exercise the whole 30 to 35 minutes and they actually work up a better sweat than [they] would during a regular PE class because they were having so much fun," she said.

Experts say physical fitness and weight aren't to be taken lightly. The comforts of modern society and a culture of rich eating mean more children become dangerously fat every year. According to the American Obesity Association, weight problems cause 300,000 or more deaths and cost $100 billion per year. And the head of the Centers for Disease Control and Prevention predicted in 1999 that 60 percent of chubby kids between the ages of five and 10 are at risk for heart disease.

"It's an epidemic, really," said Dr. Jay Noffsinger, a professor of pediatrics at the St. Louis University School of Medicine and director of pediatric sports medicine at Cardinal Glennon Children's Hospital. "Kids spend too much time sitting [in] front of the television and computer and PlayStation and Game Boy, and they don't deliver the newspaper and they don't even walk the three to eight miles to school."

Traditional sports are often not the best way for a child to get exercise, he said. Only the best players in many competitive games get to play regularly, while the others are relegated to the bench. Aerobic classes might offer a more consistent workout. But as anyone who's cared for kids knows, getting children to do something they don't like is close to impossible.

"Before the age of 6 they have to have as much fun as possible," Noffsinger said. "They have to think it's free play."

That's where the kid vids come in. Favorite figures such as Sesame Street's Elmo or Barbie (voiced by a young Jennifer Love Hewitt) have all donned legwarmers and become benevolent drill sergeants to regiments of plump pups.

That target audience became even younger in March when the Teletubbies got in on the action with their own exercise video. The television show is designed for children as young as 6 months old, and the video was designed with the help of pediatricians to let even the tiniest tots do takes on Olivia Newton John circa 1981.

"You want to jump? You jump. You want to skip? You skip," said Kenn Viselman, chairman of The itsy bitsy Entertainment Company, which licenses the show in the U.S. "It's 30 minutes of jumping and skipping. And there are no movements here that children can't do."

Those who want to take instruction from someone more, well, hard-bodied than Tinky Winky or Laa Laa have merely to say the magic words: "Billy Blanks." The video Tae Bo Jr. takes tykes through the best-selling amalgamation of Tae Kwon Do, boxing and dance.

"It's more moderately paced, and the combinations are a little simpler than they are in an adult Tae Bo workout," Tae Bo instructor Michele Reber said from her office in Canton, Ohio. "My son started doing it when he was 2 ½. He loves watching Billy."

And then there's the Tampa, Fla., mom-and-pop videos. When Michael and Janine Schwartz couldn't find a single video in their area for their overweight 8-year-old, Austin, they decided to make their own, which they sell through their Web site, www.exerciseforkids.com.

The couple cast a diverse group of kids, hired a music company to write 22 original songs, hired certified aerobics instructors and created two volumes of Movin' & Groovin': Fitness for Kids, one for kids 4 to 8 and the other for kids 8 years old and up.

With children's short attention spans in mind, the videos were designed so each song is only two or three minutes long and so there are constant set changes, from a city set with an exercise to a Caribbean set with calisthenics calypso, for example.

"If the kids say, 'I don't want to do this,' just let them sit and watch it and you'll be amazed," Michael Schwartz said. "By the third song they'll be up there."

Strangely enough, some of the biggest fans of the tapes are the senior citizens from a local retirement community, he said, leading the couple to jokingly ponder branching out.

"The next video we'll do is Exercise for Dogs," he said.