Not only will they add water back into your system, sport drinks restore potassium and other essential electrolytes (a salt substance, such as potassium, sodium, and chlorine found in blood, tissue fluids, and cells that carry electrical impulses). For children, these adult drinks may be too harsh, so talk to your pharmacist about pediatric rehydration drinks now on the market.
Don't depend on sport drinks or soft drinks for all your fluid requirements. They can come with side effects and calories. Plain old water is the best choice. Yogurt or cottage cheese both have sodium and potassium for replacing electrolytes as well.