In an article on the Moms Team website, Brooke de Lench takes a look at whether water or sports drinks are better for hydrating kids in sports:
This article includes a really comprehensive and detailed chart comparing water and sports drinks, as well as links to other related articles.
A number of studies in recent years have shown that sports drinks re-hydrate kids who are active in the heat better than water. Given a choice, kids will drink a lot more of a sports drink than of a glass of water.
An oft-cited 1999 study in the Journal of Applied Physiology reported that drinking a properly formulated sports drink with carbohydrates and electrolytes (sodium and potassium) increased fluid intake by nearly one-third (32%) compared to water. Because they taste better than water, sports drinks encouraged kids to keep drinking until their fluid needs were met.