Fact Number One:
Ask a youth player to hydrate before a soccer game and you always get the same answer. "I'm not thirsty." They simply don't understand this action or need. This is not good since young athletes typically ONLY drink when they are thirsty. 

Fact Number Two:
Most youth players don't get to eat well prior to evening practices. Most have a "school lunch" then a snack at home prior to coming to practice. Not a well balanced diet for any age of athlete. Consuming carb reserves and fluids 4 - 8 hours prior to a game is one of the most important times. 

Fact Number Three:
Give a youth player a bottle of water 3 hours before a game and they will take a few sips. Younger players consume based on taste NOT need. Using a GOOD flavored sports drink helps them take in more fluid.

The summary...
You can lead a horse to water, but you can't make him drink.  Using a bit of deception and forethought will help young athletes not only perform better, but recover quicker and be healthier.

The "general rule" we use?
Let the players pick what drink they want based on taste, then ask them to drink an entire individual size bottle (small bottle) 8 - 12 oz 2 - 4 hours prior to a game. This creates a fluid, carb and electrolyte reserve that has plenty of time digest and start to work its way to the muscles and other organs. Carbs and fluids are the key to most younger players. Most younger players don't exercise over 90 minutes. According to a recent report in the journal Sports Medicine , added sodium and potassium won't do you much good unless you're sweating profusely for more than four hours. 
We are starting to look into the new drinks with whey protein added. 
One of my concerns for my child is the lack of quality protein he eats. A pounding work out without offering some proteins for muscle growth and repair seems to me to be a recipe for a little trouble.