General Daily Fluid Requirements:

4- to 8-year-old children need about 7.5 cups of fluids per day 
9- to 13-year-old females need about 9 cups of fluids per day 
9- to 13-year-old males need about 10 cups of fluids per day 

On high-activity days, the timing of hydration becomes an extra important factor. As general rules of thumb, the following guidelines can be helpful:  

• Before Exercise: Drink 16 ounces of water two hours before activity begins and another 8-16 ounces right before exercising.
• During Exercise:  Every 15-20 minutes, drink at least 4-6 ounces of fluid during vigorous exercise. For less vigorous exercise, decrease the amount slightly.
• After Exercise: Drink 16-24 ounces of water for every pound lost during physical activity. Consuming rehydrating beverages (like fruit smoothies) and eating watery foods (such as fruits and vegetables) along with salty ones can help replace lost fluids and electrolytes.