We went a few days after Easter one year to celebrate our son's 5th Birthday (which was 2 days after Easter). It also happened to be spring break that week for a lot of people. Fort Wilderness was mobbed, we had to call back for 2 weeks just to get in for 2 nights. We only did Magic Kingdom and it was very crowded too.
I don't have any specifics but FW and Disney do have special events for the various holidays. At FW it can be as simple as a golf cart parade or Easter Egg hunt. Some of the resorts have special buffets or Epcot may have an Easter buffet. Check some of the Disney boards as stated above for further details.
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We were there last year at Easter. I believe there were Easter Egg Hunts and other activities but we didn't participate. The campground was quite busy (especially the pool area) but the park (went to AnimalKingdom) really didn't seem that crowded (not even comparable to this year at XMas). That said, Easter was quite late last year, this year it's a bit earlier so you might catch some of the late spring breakers (although 1st week of April is probably still safe).