HYDRATE!

The grass isn't the only thing that needs water in this weather. Guys your age usually lose 1.5 litres of sweat per hour when performing intense soccer activities in heat like this. a study last year showed that nearly two thirds of the soccer players being tracked were showing up for practice already dehydrated. It is extremely important to be drinking plenty of fluids before practice and after practice as well. The U.S. Soccer Federation recommends: "that parents and coaches ensure children are well hydrated before practice and games. During activity, young athletes should drink on a schedule; because thirst is not an accurate indicator of fluid needs, athletes should drink before they become thirsty."

You need to be aware of the signs of heat illness. If someone becomes unusually fatigued, dizzy, and nauseous or has a headache during exercise in the heat, have them stop, rest and drink fluids

Here is a link to the United States Soccer Federation's guidelines.