The most important factor is that your athletes have a good supply of energy ready to go to work in their muscles. A meal relatively high in carbohydrate is the best choice. Keep the levels of fat and protein low since they take longer to digest which can result in nausea or even vomiting. Some athletes get so excited before an event that it interferes with digestion. It is best to eat well beforehand, that means no closer than two to four hours before practice or competition.
Digestion requires routing the blood supply to the digestive tract to pick up nutrients.
By the time exercise begins, the blood should be freed of that task so it can focus on the more immediate job of carrying oxygen rich blood to exercising muscles. The energy supplied to and stored in muscles for use during exercise was put there hours or days earlier. Simple sugars like candy or soda eaten just prior to an event may cause an interfering swing in blood sugar levels that could adversely affect the child's performance without providing that quick energy you thought it would. Don't forget the fluids. Add apricots and whirl just to chop coarsely.