Children as young as age 7 are being put on diets.  Is this too young?  From ABC:

When Dara-Lynn Weiss's daughter Bea went for her annual checkup at age seven, the pediatrician pronounced her obese. In one year, Bea had gained 23 pounds and her blood pressure had bumped up significantly.

"This was a health crisis," Weiss said.

Weiss's solution was to put Bea on a calorie-restricted diet, an experience she chronicled first in a magazine article then in a bestselling book, "The Heavy."