When the concerned mother took her plump, junk-food addicted son to the doctor for his annual school physical, she posed this question: Should the nine-year-old be placed on a diet? The youngster's Montgomery County soccer teammates teased him about being fat as he puffed down the field during games. Even the boy himself had voiced tearful concern about his weight.

"Don't worry," the doctor replied. "He'll grow out of his baby fat."

The overweight boy did indeed grow. Today, at age 10, he carries 111 pounds on his 4-foot-9-inch frame and is now obese -- a classification determined by being 20 percent or more above the average weight for boys his age and height. Odds are he will carry those extra pounds with him for the rest of his life, since more than half a dozen studies show that 60 to 70 percent of chubby 10- to 13-year-olds become overweight adults. And because heavy children often have elevated blood pressure and serum lipids -- high levels of cholesterol and triglycerides -- researchers also believe that these youngsters may be on a collision course with hypertension and cardiovascular disease as adults.

But a new behavioral therapy program, which strives to change health habits and features a special Stoplight Diet for children, may help obese youngsters solve their weight problem for life.

Developed by psychologist Leonard Epstein and his colleagues at the University of Pittsburgh's Western Psychiatric Institute and Clinic, the diet teaches children to classify foods according to the signals on a traffic light. High calorie foods are labeled red; moderate calorie foods are considered yellow and low calorie foods are green.

Changing health behavior "may be easier for kids to do than adults," says Epstein. Adults find it "very difficult," he says, to alter eating habits, increase exercise, give up cigarettes and cut alcohol intake.

Based on findings from his five-year program -- which stresses nutrition education, exercise, family involvement and the Stoplight Diet -- Epstein feels "that effective treatments for childhood obesity are on their way."

Youngsters in the study came from 76 families in the Pittsburgh metropolitan area. The children had at least one obese parent -- a condition that makes them even more likely to be fat adults than overweight children with thin parents, Epstein says.

Study participants were 8 to 12 years old and weighed on average 40 percent more than the norm for children of their age, height and sex. All families paid a $65 deposit which was refunded if they successfully completed their portion of the contract.

Treatment consisted of eight group meetings over a two-month period, which included instruction in the Stoplight Diet. Children were limited to no more than four high-calorie "red" foods a week. They learned to keep records of what they ate and were encouraged to choose lower calorie -- "green" or "yellow" foods -- instead of "red." Adherence to the diet and exercise regimens earned children points which could be used to "buy" privileges such as staying up later.

Children were placed at random into one of three groups. In one group, both parent and child agreed to lose weight by using the Stoplight Diet. In another, just the child dieted, again using the Stoplight approach. Finally, in the third group, both parent and child were encouraged to lose weight but not required to do so as part of the program. The only requirement for this group was that they attend group meetings where children and parents learned about the Stoplight Diet, nutrition and exercise.

Initially, "all the children lost the same amount of weight," Epstein reports. But five years later, significant differences emerged between the groups, underscoring the importance of behavior modification and family suppport. Children who dieted with their parents were the most successful at losing pounds -- and keeping weight off. About "40 percent of these children have been able to maintain normal weight for the past five years," Epstein reported earlier this month at the annual meeting of the Association for the Advancement of Behavior Therapy.

Youngsters in the other groups fared much worse. Those who dieted alone were more overweight five years later than when they began the study. Children from the third group who had learned about dieting, but weren't required to do it, ballooned even more: they gained twice as much as the group that dieted without a parent.

"Based on the results of this study, both a strong behavioral modification program and structured family support seem to be necessary for successful weight control," Epstein says.

Even when adults put pounds back on -- and by the end of five years all parents in the study were back to their pre-diet weight -- children who began dieting with their parents still maintained normal weight.

"Even though the parents were regaining weight themselves," Epstein says, "they seemed able to support the kids in their diet."