According to the Centers for Disease Control and Prevention, 16 percent of all children and teens in the United States are overweight.
The rate of obesity in the United States has more than doubled for preschoolers and adolescents, and it has more than tripled for children ages six to 11. (Source: “Childhood Obesity: What Parents Can Do.” Mayo Clinic Staff, April 19, 2005.  www.mayoclinic.com/health/childhood-obesity/FL00058)
Some groups are at greater risk, according to a national study, from 1986-1994, overweight prevalence rose by more than 120 percent among African-Americans and Hispanic children, compared with more than 50 percent among whites. (Source: Strauss RS, Pollack HA, Epidemic increase in childhood weight. JAMA. 2001; 286:2845-8.)

Some general facts about the prevalence of childhood obesity nationally.