I like the monorail resorts for convenience, but I think the resorts that have DVC villas seem to have more children's activities. We stayed at Boardwalk with 3 YO DS (and previously, with 3 yo DN) and they loved it. Lots of activities at the pool and rec center, the evenings are lively with lots of entertainment on the boardwalk. Also, DS loved the boats that went to and from epcot and DS. On the same week we were there, friends were at Poly with their similarly aged kids, and their kids didn't like it- said no kids' activities, the year before they were at WL and said there were lots of kids activities- again, WL has a DVC.
Either way, you can't lose with a disney deluxe resort!