If your pre-schooler still naps, I'm partial to resorts that are on the monorail for the simplicity of going back and forth to the parks, specifically the Magic Kingdom. With that in mind, I like the Polynesian because it is easy to get to the Magic Kingdom by monorail/boat, but it also as equally convenient to get to Epcot by walking to the Ticket and Transportation Center to take the Epcot monorail.
The rooms are some of the largest at WDW, so there is plenty of extra room for strollers and play space for restless little ones. In fact, we prefer rooms on the first floor so our children can go out in the lawn and play when they need to burn off some energy. We also think it is a quiet resort so the evenings and nap time are not interrupted with foot traffic and other sounds.
Additionally, the pool is a zero-entry pool, so it is incredibly friendly for children of all sizes and also has a water play area next to the pool. The pool is located right on the shores of the Seven Seas Lagoon, so kids can enjoy play time in the sand as well.
The resort offers plenty of activities for children during the day and has a wonderful kids' club. My sons always ask what night they get to go to the Neverland Club when we visit WDW because they enjoy it so much.