Hit the parks EARLY, the suggestion about a sit down restaurant midday is great, that's what we do for our big meal is a late lunch, lunch prices, dinner quality, and gets us in out of the heat; we find it better than a nap in the room.
Use the water parks or pools for afternoon relief, Park attendance drops in the evening, so a great time to go back and get the benefit of people who hit it too hard during the heat.
Go with the flow, and try not to think you can do it all. We find it is usually cooler there even in August than here at home (kansas) so not usually a big issue for us.
Have a great trip!!!
k