We started going to the parks when my kid's were 4 and 6 - and they were just as happy jumping on the hotel bed and playing in the arcade. At that age, some of the things we used to do (and avoiding the parks were:
1) Character Breakfasts / Lunch outside the park. We always felt that if we had a character meal in the park we were losing park time. So, we scheduled if for our non-park days.
2) All of the
DVC resorts have a recreation staff and they usually have one or multiple activities (unbirthday partys, Colering, etc.) each day.
3) We always tried to schedule at least one Pool Hoping day as both the kids loved to swim.
4) Buy a Hidden Mickey book - that alone will occupy allot of time - the kid's love it, and, you get to see some of the different resorts.
5) The boat rentals were also a yearly favorite.