How young? If they are strong and sensible, and you are confident to let them swim alone, Beach Club. The reason for the caveat is Stormalong Bay is like 5 different pool areas in a mini-waterpark. You can't keep an eye on them, so you have to be sure enough of them as swimmers and sensible kids to allow them to basically go off on their own, unless you swim beside them the whole time of course. But it is very nice, if the kids are old enough. And bonus, it is walking distance to 2 parks, and all the dining options of Epcot and the Boardwalk, and boat transportation too.