Easter Sunday there are Easter egg hunts or similar at the resorts (characters there and usually the Easter Bunny; some like BW also have craft events. At the parks, you may see some extra displays like at some of the nations in Epcot, but otherwise nothing happens at the parks that does not happen other days of the week during the holiday. MK is traditionally the most crowded park that day (and can reach capacity) leaving the others with what is often their lightest day of the holiday season (still very crowded but not completely overwhelming like other days)