We were there last week on Easter Sunday and the 6 days after (that's when our Spring Break is). I was expecting the crowds to be horrible.... I was pleasantly surprised.
Since my kids (DD is 6, DS is 4) get up early (around 6:30 am), we stayed on schedule and were at the parks as soon as they opened. We got a lot done before 11 am. After that, Epcot, AK, and MGM were still okay. On the MK days, we went back to the hotels in the afternoon and napped/played in the pool. Luckily, we planned to do that so we weren't frustrated. The crowds in MK- especially FantasyLand- were huge but not as bad as I expected.