When people play in the heat, they sweat. Perspiration acts like a natural air conditioner; however, this system can fail if you overexert yourself on hot and humid days, resulting in heat exhaustion or heat stroke. During activity, your body uses large amounts of water and it's easy to become dehydrated.
To prevent dehydration, you and your children should drink about a cup of water every 30 minutes on hot days. Give the kids their own plastic water bottles to encourage drinking before, during, and after activities. Limit caffeinated and sweetened beverages, which can deplete the body of water.