Objective To test the impact of obesity on health and health care use in children, by the use of various methods to account for reverse causality and omitted variables. Data Sources/Study Setting Fifteen rounds of the Health Survey for England (1998–2013), which is representative of children and adolescents in England. Study Design We use three methods to account for reverse causality and omitted variables in the relationship between BMI and health/health service use: regression with individual, parent, and household control variables; sibling fixed effects; and instrumental variables based on genetic variation in weight. Data Collection/Extraction Methods We include all children and adolescents aged 4–18 years old. Principal Findings We find that obesity has a statistically significant and negative impact on self‐rated health and a positive impact on health service use in girls, boys, younger children (aged 4–12), and adolescents (aged 13–18). The findings are comparable in each model in both boys and girls. Conclusions Using econometric methods, we have mitigated several confounding factors affecting the impact of obesity in childhood on health and health service use. Our findings suggest that obesity has severe consequences for health and health service use even among children.