Call it the sunshine paradox: Kids may be most at risk of packing on pounds during summer, that prime time for swimming, hiking and bicycling...

Call it the sunshine paradox: Kids may be most at risk of packing on pounds during summer, that prime time for swimming, hiking and bicycling, researchers report.

But instead of taking on those high-energy pursuits, many kids are cooped up playing video games and munching calorie-laden snacks.

A new study highlighted the summer weight-gain phenomenon among young children. Researchers in the Midwest looked at the body mass index, which relates height to weight, of 5,380 students. They followed them for two years, from kindergarten through first grade, and found the average index grew more than twice as quickly over the summer than during the school year.

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Children of the working poor may be especially at risk because they are left indoors while their parents are at jobs. While at home, kids eat and drink what they want, says Dr. Jennifer Bass, a pediatrician who chairs a national pediatricians special-interest group on obesity. Bass estimates as many as 30 percent of her patients are overweight.

“What fills up all those extra hours?” Bass says. “Often it can be TV or video games.”

Bass recalls one 6-year-old whose older sibling baby-sat her while her mother worked. Neither was allowed outside while their mother was away. Even at 6, the child was obese.

“I said, ‘So what are you doing?’ ” Bass remembers. “She said, ‘I’m watching a lot of TV.’ I said, ‘Ideally, it would be good to limit it to one or two hours a day.’ And they were just laughing at me.”

The health consequences of childhood obesity are significant. Daniel Marks, an Oregon Health & Science University pediatric endocrinologist who studies and treats obese children, says many of his referred patients come with orthopedic problems, Type 2 diabetes and sleep apnea. The youngest child referred to him for morbid obesity was not quite 1 year old.

“I, of course, see the worst of the worst,” Marks says. “I’m really starting to see children, even under the age of 10, developing diseases that would usually be seen in adults.”

According to estimates from the federal government’s Centers for Disease Control and Prevention, without intervention, 1 in 3 children born in the year 2000 will develop diabetes.

Unlike with other health problems, treatment of an overweight child means changing the entire family’s behavior. That’s not easy, doctors and researchers say. Parents usually have their own weight problems, and act as poor eating and exercise role models for their children.

Bass conducted a study while working in New York that showed 50 percent of parents with obese kids didn’t recognize their child as overweight. Even doctors might minimize the child’s weight problem or fail to mention it.