Hyatt Grand Cypress has a killer pool (huge, has water falls that you can swim through and a nice slide and is open 24 hrs a day), as well as other activities that are included in your daily resort fee (boating, biking, rock climbing & pitch and putt golf). Another hotel is the Hilton Bonnet Creek. They have a lazy river and a slide.
Forgot to mention, I do not recommend Hyatt Grand Cypress if you have younger children that cannot swim or cannot swim well, as some of the areas in the pool are over 6 ft deep. Hilton Bonnet Creek doesn't get deeper than 4 ft.