In moderation, these drinks are not a problem. However, the sugar content might not provide them with the energy boost for exercise that they think they are receiving from it. However, if youngsters have consumed these beverages regularly, they may not feel any negative effects. Yet, if they are weaned from the sweet sodas, they would probably feel the difference physically and mentally, eventually.
Water is fine sport drink in most cases.
However, in prolonged activity lasting more than an hour, an electrolyte replacement drink is superior to plain water.