I'm going, for the 3rd time, to Super Soap Weekend. It is held in MGM only, on Saturday and Sunday only. In my experience, MGM is very crowded on these days, and people stay in the park most of the day, waiting for their Fast Pass times to meet the stars. The other parks are not involved, so probably better for your boys---assuming you are not interested in the Super Soap events!
One other thing to remember that weekend--it is the last weekend of the Food and Wine Festival at EPCOT. In the evenings, I believe EPCOT will be more crowded than usual.