The intensity of activities that last 15 minutes or more should be reduced whenever high heat or humidity reach critical levels.
At the beginning of a strenuous exercise program or after traveling to a warmer climate, the intensity and duration of outdoor activities should start low and then gradually increase over 7 to 14 days to acclimatize to the heat, particularly if it is very humid.
Before outdoor physical activities, children should drink freely and should not feel thirsty. During activities less than one hour, water alone is fine. Kids should always have water or a sport drink available and take a break to drink every 20 minutes while active in the heat.
Clothing should be light-colored and lightweight and limited to one layer of absorbent material to facilitate evaporation of sweat. Sweat-saturated shirts should be replaced by dry clothing.
Practices and games played in the heat should be shortened and there should be more frequent water/hydration breaks. Children should promptly move to cooler environments if they feel dizzy, lightheaded or nauseous.
Adapted from aap.org