Go to WDW during Spring Break time. As we live only about an hour away and can make day trips just about any time, its a no-brainer to avoid the busiest times.
Well, this year I took a few days off from work in March, and told DS, who is 3, that on one of the days he could pick out something special he wanted to do. I thought he'd want to go to Chuck E Cheese, or maybe the zoo or the aquarium, but he chose to go to WDW! We spent the day at MK in the middle of the biggest crowds I have ever experienced. I can definately say it something I will never do AGAIN.