SandraC,
It is definately hot in Disney in August, but I don't find it to be intollerable, there is always some way to cool off, like most rides and the shops. I allways go to the parks in the early am, and then when it starts to get really hot, I go back to the hotel for a swim or nap and come back in the evening when it starts to cool down some. Also swimming cools down your body temperature.
I took my one yr old son last Aug. and just used the water bottles and drank plenty of fluids. We had a blast. Let me know if you have anymore questions!!