Purpose This study examines changes between 2003 and 2007 in obesity and overweight prevalence among U.S. children and adolescents 10 to 17 years of age from detailed racial/ethnic and socioeconomic groups. Methods The 2003 ( N = 46,707) and 2007 ( N = 44,101) National Survey of Children's Health were used to calculate overweight and obesity prevalence (body mass index BMI ≥85th and ≥95th percentiles, respectively). Logistic regression was used to model odds of obesity. Results In 2007, 16.4% of U.S. children were obese and 31.6% were overweight. From 2003 to 2007, obesity prevalence increased by 10% for all U.S. children but increased by 23%–33% for children in low-education, low-income, and higher unemployment households. Obesity prevalence increased markedly among Hispanic children and children from single-mother households. In 2007, Hispanic, non-Hispanic White, and American Indian children had 3.0–3.8 times higher odds of obesity and overweight than Asian children; children from low-income and low-education households had 3.4–4.3 times higher odds of obesity than children from higher socioeconomic households. The magnitude of racial/ethnic and socioeconomic disparities in obesity and overweight prevalence increased between 2003 and 2007, with substantial social inequalities persisting even after controlling for behavioral factors. Conclusions Social inequalities in obesity and overweight prevalence increased because of more rapid increases in prevalence among children in lower socioeconomic groups.