Hi @seabass15! Since you book FP in the am, I wanted to add one more perspective.
Our first family trip with (at the time) DDs 9, 6, and 2 we allotted 2 MK days and a day each at every other park. At the end of our week, we tacked on another park day (since we were driving and were flexible and additional park days are SO cheap to add while you’re there). We let the kids pick which park to visit one more time, and they picked one more day at MK.
All that to say, 3 MK days is definitely not unreasonable for a family with kids your age.
BUT, I’ll say this: one mistake we made is not budgeting a full day of no park touring. I almost wore our family down with our aggressive touring schedule. This next time, I’m scheduling one full resort/rest/swim day.
Also, in line with what others have said here, I didn’t feel like we got in enough time at Epcot. Even though all the kids voted for one more day at MK, Epcot is actually my oldest daughter’s favorite park. If I had all the time in the world to play with, I would do 2 or 3 days at MK, and then a day and a half at Epcot, and then a rest day and then add a day each at the other two parks.
One more thing: I know others advocate for starting your trip with MK, but we actually like to start our trip with Epcot. It lets us get our sea legs under us and then build up to MK.
Regardless of what happens in the morning, your trip is going to be GREAT and I’m so excited for your family!