If you want to try the Epcot resort area and your kids would like a smaller slide, you could think about Beach Club and Stormalong Bay. When my three were too small for the big slide, they really enjoyed the little slide that they have across the path at Stormalong Bay. there are two slides there - the big one, and the small one that is with a smaller shallower pool. You can easily grab the kids at the end of that slide, something not allowed at the big pools. Also, the shallow sandy area is so fun. My kids just loved sitting and playing in that water. Now the pool area is huge and if your older child wants to enjoy the big slide and the lazy river, then your family will have to split up because there is no way to keep an eye on all three kiddos if they are enjoy different areas.
We love the Boardwalk Inn. My kids love how quiet and laid back the pool area is. It really helps them wind down after a busy morning at the parks. We'll be staying at the Boardwalk Villas again this summer and I can't wait! Enjoy planning your trip.