Hi Kelly,
The best pool on property is
Stormalong Bay in my opinion. It is a mini-water park with a sand-bottom pool. It has a small lazy river and an awesome water slide. My kids could spend an entire day there; my 5 year old could spend an entire vacation there. Stormalong Bay is shared by Disney's Beach Club and Yacht Club Resorts. They are located on Crescent Lake, between Epcot and Disney's Hollywood Studios. They are across the lake from Disney's Boardwalk, giving you easy access to the shops, restaurants, and night clubs there. You are also in luck, because you can stay at the Beach Club Villas, the Disney Vacation Club (DVC) portion of the resort, which has rooms with a kitchen. My family and I stayed in a 1 bedroom Deluxe Villa last summer and we loved it. You do not have to be a member of DVC to stay in a DVC resort.
My next recommendation would be to stay in the
Kidani Village portion of Disney's Animal Kingdom Lodge. It is also a DVC property and you can get a villa with a kitchen there. They also have a pool area that most would call a mini-water park, though I think Stormalong Bay at the Beach Club is better.
Also, be sure to consider spending a day at Typhoon Lagoon or Blizzard Beach. The water parks are fabulous. We have visited Walt Disney World before with the sole intent of spending the entire vacation at those two parks. They are absolutely fabulous. My family prefers Typhoon Lagoon over Blizzard Beach, but I know many families who would say the exact opposite.
Enjoy planning and write back if you have any more questions!