Hook hit the important info, but do take time to cool off on the water ride, Journey to Atlantis as well in Shamu's Happy Harbor. They have a "wet" area for kids to run around in with water blasters and sprinklers, I've been in there to cool off too!
As for Aquatica, stay all day! The place really empties out around 5-6pm. I think they're open till 9 this summer so take advantage of the place when it's not crowded. Most slides are designed for two or more people. Only a few are singles only. so this gives the family more time together. Note, as with everywhere, the eateries are packed between 11-1 for lunch. Avoid 30 minute waits for food by snacking/early or late lunch. If our famous thunderstorms come up, just ride it out.
If you're staying in Orlando, take the shuttle to Busch Gardens. Be sure to see all the animals, and know things will be different with all the construction going on right now for their 2011 project. The shows there are not "must sees" but they might offer air conditioning!
Just enjoy your time and have fun. If you have any specific questions about the old beer parks, send me a PM.