100 WITH the heat index? Try it without the head index.
Everyone keeps telling you water. But you probably already go between games for water. It's important that you find a way to make water available between innings. Heat stroke or Heat Exhaustion can come on quick. A big thermos with a strap, with water and ICE, tied to the screen to keep it off the ground is what I do. Just a little bit between every half inning, or even DURING a very long inning, makes all the difference. The crushed ice in the water helps more than just water.
Plus I'll grab a gatorade between games.
Also - watch out for your catchers, especially at lower levels. These coaches don't know what they're going through, and the kids don't know enough to say something in the middle of an inning. If you're wanting water during an inning, they are too. Make sure they get it.
Worked a tourney a few weeks ago (it was over 100 and no wind at all) where we were even letting the coach bring water to the pitchers during innings, as long as they didn't coach.