How will your kids be after traveling? Do you have an early wake up to get to the airport or will they nap on the plane?
When my kids were in the age ranges of yours, we spent the majority of our time at MK, followed by AK, and HS and EP last. We would tour hard at MK and still need 2 days to get through all of it at least once. My kids (and my wife and I) had no interest in the world showcase at Epcot and no one was ever happy when we ventured that way in that park. On our trips, we would designate 1/2 day visits to Epcot to do the rides/shows that the kids liked and we liked but I think what you have planned is a good plan if you think that a single MK day is enough? Good luck.