Summer heat is responsible for a significant number of illnesses and emergency department visits. Although more common in elderly patients, infants, children, and adolescents are also vulnerable. Those involved in the care of pediatric patients need to be aware of the differences in physiology and behavior, as well as predisposing factors that put children at risk. Heat illness constitutes a spectrum of maladies, ranging from the very mild and irritating prickly heat, to severe and potentially life-threatening cases of heatstroke. Milder forms of heat illness respond to removal from the hot environment, rest, and hydration. Heat exhaustion and heatstroke must be recognized early, and rapid cooling and fluid resuscitation must be initiated promptly. Many cases of heat illness can be prevented by paying careful attention to the type of clothing worn, gradual acclimatization to hot and humid conditions, limiting exposure during the hottest part of the day, and drinking fluids both before and during outdoor play or exercise.