If the kids are good enough swimmers that you can trust the lifeguards and not watch them every moment, then I'd recommend BCV. (As you've probably heard, its wonderful pool is so sprawling and filled with interesting eddies that it's easy for kids to wander out of sight of your deck chair.) You also get the advantage, if you have an all-parks pass, of popping in and out of Epcot--which has a lot of restaurants--for the main meal each day.