I would feel odd if I went to Disney and didn't go to all of the parks at least once, however that is just me. We tend to do Mk 2 days, Epcot 1 1/2-2 days, DHS 1 day, and AK 1 day.
With children those ages I would suggest 2 MK, 1 AK, 1 DHS. While there are attractions for children in Epcot, I...