I think you made the right decision! Take the kids to UO when they're older (at 10 they should be able to ride everything. My nephew is 8 and could do most things)
To add to my comment from earlier we did the 3 days at UO and the magic kingdom and epcot back to back for a total of 5 days. Hello exhaustion lol
My nephews are 8 and 10 and you could tell they needed like a day break between each park. They started to melt down mid week.