“We may see the first generation that will be less healthy and have a shorter life expectancy than their parents,” U.S. Surgeon General Dr. Richard H. Carmona recently told a Senate committee.

Obesity is poised to pass tobacco as America’s leading preventable killer, and it’s a growing epidemic among children. Hospital weight clinics are treating preteens and teens who weigh as much as 400 pounds. Over the past 20 years, the proportion of overweight children doubled among 6- to 11-year-olds and tripled among adolescents ages 12 to 19.

One in seven kids — more than 9 million children — are overweight, according to the Centers for Disease Control and Prevention. Ten percent of 2- to 5-year-olds weigh too much.

Excess childhood weight is placing “an unprecedented burden” on children’s health, according to the American Academy of Pediatrics. It’s triggering a host of dangerous health problems once seen only in adults.

Being overweight isn’t a phase most kids outgrow, either. Overweight adolescents have a 70 percent chance of becoming overweight adults.

“The good news is that there is still time to reverse this dangerous trend in our children’s lives,” says Julie Lindsay, a registered and licensed dietitian at Children’s Medical Center Dallas. But to do that, we need to understand why so many children weigh too much.

Genes play a role for some children, but that’s not new. The world kids live in is new in many ways, though.

“More than 40 percent of a family’s food budget is spent on food consumed outside of the home,” Lindsay says. “Soft drinks and 10 percent juice drinks account for more than 10 percent of adolescents’ caloric intake.”

The average child spends 5 1/2 hours a day watching TV, playing video games, and using computers and the Internet, according to the Kaiser Family Foundation.

Sometimes, kids learn unhealthy behavior from us. Many overweight parents don’t feel anything’s wrong when their children become heavy. Other parents worry more about different things. In a recent Ohio survey, for instance, parents listed sexual activity, alcohol consumption and cigarette smoking ahead of weight problems when asked about their top health-related concerns for their children. And still other parents don’t know how to solve the problem.

“The key is to have a concerted effort to change not only the culture but the perception that obesity is an unstoppable disease. It is preventable,” Lindsay says. “And it’s a lot easier to do it when you’re a child than someone much older.”