Despite the benefits of smoke-free legislation on adult health, little is known about its impact on children's health. We examined the effects of tobacco control policies on the rate of emergency department (ED) visits for childhood asthma (N = 128,807), ear infections (N = 288,697), and respiratory infections (N = 410,686) using outpatient ED visit data in Massachusetts (2001-2010), New Hampshire (2001-2009), and Vermont (2002-2010). We used negative binomial regression models to analyze the effect of state and local smoke-free legislation on ED visits for each health condition, controlling for cigarette taxes and health care reform legislation. We found no changes in the overall rate of ED visits for asthma, ear infections, and upper respiratory infections after the implementation of state or local smoke-free legislation or cigarette tax increases. However, an interaction with children's age revealed that among 10-17-year-olds state smoke-free legislation was associated with a 12% reduction in ED visits for asthma (adjusted incidence rate ratios (aIRR) 0.88; 95% CI 0.83, 0.95), an 8% reduction for ear infections (0.92; 0.88, 0.97), and a 9% reduction for upper respiratory infections (0.91; 0.87, 0.95). We found an overall 8% reduction in ED visits for lower respiratory infections after the implementation of state smoke-free legislation (0.92; 0.87, 0.96). The implementation of health care reform in Massachusetts was also associated with a 6-9% reduction in all children's ED visits for ear and upper respiratory infections. Our results suggest that state smoke-free legislation and health care reform may be effective interventions to improve children's health by reducing ED visits for asthma, ear infections, and respiratory infections. (C) 2016 Elsevier Inc. All rights reserved.