Oh, boy. So many choices here. I guess we'd need to know how into thrill rides your kids are. If meet and greets are important. Etc.
My kids, when they were 4 and 5, BTMRR was as crazy as they'd get. So, in MK, I'm guessing 7DMT is top of the list, then, if they're into it, BTMRR, and finally Peter Pan gets such huge lines, its a wise use of FP. Others on that list would include Winnie the Pooh, ETWB, Speedway, Splash Mtn (if not too scared and the weather is right), etc.
Epcot, with the tiered structure you pretty much have to go with Frozen if you want to do the ride. There's other ways, but I'd go that route. Then the rest is kinda up to you. If you wanna do TT and Soarin', you'll have to rope drop one of them (probably TT), and get the other one when standby is low (probably Soarin' since its got an additional screen now).
AK, for me, Safari is first priority. Expedition Everest also is a good use, but your littles might be TOO little. And Kali would be my other recommendation.
DHS - here again, depends on what your littles can handle and how tall. ToT and RnR are the two biggies. Might be that none of yours are into those rides, and in that case I'd be looking at Star Tours. Could split these up if the older one(s) want to do different things.
Hope any of that helps. EasyWDW has a "FP+" priority list on their website if you want to reference more.