While childhood obesity may be leveling off, a new class of obesity has grown in prevalence, according to the American Heart Association.

Severe obesity -- a newly defined class of risk -- exists in 5 percent of all U.S. children. Effective treatment options are limited for these children, who are at a high risk of developing premature heart disease and Type 2 diabetes.

“Severe obesity in young people has grave health consequences,” said Aaron Kelly, Ph.D., lead author of the statement and a researcher at the University of Minnesota Medical School in Minneapolis. “It’s a much more serious childhood disease than obesity.”

In children over the age of 2, severe obesity is defined by a body mass index (BMI) that’s at least 20 percent higher than the 95th percentile for their gender and age, or a BMI score of 35 or higher.

So, for example, a 7-year-old girl of average height weighing 75 pounds, or a 13-year-old boy of average height weighing 160 pounds, would be considered severely obese.

The statement calls for “innovative approaches” such as conducting more research on bariatric surgery, lifestyle and dietary changes.

Cardiologist Dr. Valentin Fuster, director of Mount Sinai Heart at the Mount Sinai Medical Center in New York City, says treating obese children is difficult.

"Somehow you think you've got it, but they come back," Fuster told CBS News, describing the challenges surrounding treating obese children. "We are dealing with a problem." He added: "This is why it's so important to know the reasons for why you're obese."

According to the U.S. Centers for Disease Control, roughly 17 percent of children and teens between the ages of 2 and 19 are obese. The prevalence has tripled since 1980, and studies show significant racial and ethnic disparities in children who are overweight. For instance, Hispanic boys are more likely to be obese than non-Hispanic white boys.

Obese children in the U.S. have higher rates of Type 2 diabetes, high blood pressure, high cholesterol, liver disease, sleep apnea, musculoskeletal problems and early signs of clogged arteries. "Those are the immediate consequences, but we also know that severe obesity in childhood is a strong predictor of morbid obesity in adulthood," Kelly told USA Today.

The AHA is pushing for a “call to action” to treat the disease.

"We are saying this is a problem that hasn't been defined really well until now, and we need to get people to wrap their heads around how serious it is,” Kelly said. “Severe obesity is an extremely difficult disease to treat. Most of the standard approaches often used successfully in children with milder forms of obesity unfortunately do not work very well in those with severe obesity."