The health burden of air pollution on the world’s children is immense. Environmental factors are responsible for an estimated 26% of all children’s death worldwide. A large body of research exists on the effects of air pollution on children’s health, including effects on fetal growth, birth outcomes, lung development and function, asthma, respiratory infection and otitis media. It is also clearly linked to a higher risk of developing asthma, a major cause of morbidity in children. Indoor environments contribute significantly to total human exposure to air pollutants. Overall, people spend most time indoors. Pollutants remain in the air longer inside than outside. Some pollutants may be two to fivefold more concentrated inside than outside the buildings; furthermore, indoor pollutants may have an important biological impact even at low concentrations over long exposure periods. Indoor air pollution represents a substantial risk for human health, particularly for children (their defense mechanisms are still evolving, and they inhale a higher volume of air per body weight than adults) and subjects with respiratory diseases, at higher risk for specific exposures, or socioeconomically deprived. Moreover, the evidence of the harm done by tobacco smoking and second-hand smoke to people of all ages is well established. Scientific understanding of the serious risks posed by air pollution early in life is robust and growing and must be translated into action. The body of evidence provides ample support for effective policy measures and suggests concrete actions for pediatricians, health care providers, and families responsible for protecting fetuses, infants and children.