With the ages of your kids, I think to feel like you hit the highlights of each park for your kids' ages, you need to have 2 days at MK, and one day at the other parks. If possible, I would add in one additional day for relaxation/perhaps going back to a park you liked for a few hours to repeat a few rides/attractions.
We have done Disney twice now. The first time, we stayed off property and only allocated one park a day in our itinerary. We went to the parks mid-morning (10 a.m.) and stayed until about 6-8 p.m. (or whenever the park closed). Our kids, at that time, were 2, 5 and 7 (our 2 year old was a very good stroller napper). While I felt pretty satisfied leaving AK and HS after one day, we still didn't get a chance to do everything or see everything. With MK and EP, there were many things we didn't get a chance to do or see, but we hit the highlights that were age-appropriate for our kids.
This past trip (kids then aged 5, 8, 10), we stayed on property for 7 nights. This time, we got to the parks around 9-10 a.m. and stayed until about 7-8 p.m. (no naps). It took us a good 3 days to do MK and see *everything* (there are only 2-3 things we haven't done now in MK), 2 days to do Epcot (there are still a few things we haven't been able to do), and 1 day again in AK and HS (again, a few things we haven't done). My kids aren't super adventurous with roller coasters and the "scarier" rides, but there were many more rides and attractions that we were able to do this time because they were older. We are booking the same number of nights for our upcoming trip: Because we were just there a few months ago, there are several things that we did that we definitely won't do again, a few things we have to do because they were closed or we didn't get to them last time, and a few things that we have to do again because we enjoy them. But we plan to take it at a much more leisurely pace and enjoy the resorts more.
I will also say that after 7 nights, I was beat and ready to get home. Even being in good shape and being physically fit, our first two Disney trips were anything but relaxing. I was glad during our last trip we scheduled some time at Hilton Head following our trip and had a few days to unwind at home before getting back to work.