I'd skip a lot of MGM. Get park hoppers and go there just for a couple of hours, for ToT and RnRC, the one show that sounds best to you, and maybe get Power Rangers autographs if the kids are into them. MGM is a huge time waster IMO because it's mostly shows, and it always seems as if, when you get out of one show, you don't have enough time to get to another before it starts. So you try to ride ToT while you wait for the
next showing, but it's line (even with FP) is longer than you'd hoped, and you still miss the next showing of the next show you want to see, and so on, and so on...

The backlot tour (or whatever it's called) is disappointing, too, especially if you've been on the one at Universal.
I'd also skip a lot of Epcot. Don't miss Soarin' and Test Track, but a lot of the rest is really dependent on your personal likes and dislikes. Our family is more into exhilarating rides, so we didn't think Living with the Land and Spaceship Earth were anything special, but lots of people love them. Innoventions can easily be skipped, it's just not that innovative anymore.
At MK, with your age of kids, I'd skip Dumbo, Aladdin, Speedway, TTA, Toontown (unless they are big into characters) carousel, teacups, Tom Sawyer's Island, Jungle Cruise, Tiki Room, the train, and some of the Fantasyland rides, depending on what characters your family likes.
At AK, I'd skip Triceratops Spin, but I haven't explored the place enough to tell you anything else. My 8yo (girl) loved Primevil Whirl, Dinosaur, and Kilmanjaro Safari, but didn't want to explore any of the trails or see any shows, so we left that park early. Hmm, she did the same thing at age 4, guess AK's just not her thing, lol. I'd love to go there by myself one day and explore the trails.
Personally, if I were you, I'd get parkhoppers, spend 2 days at MK, and make half days of whichever 2 of the other 3 are less appealing to you. But again, it really depends on your likes and dislikes, so take that with a grain of salt.
Oh, yea, and I'd skip all the parades. They take up a huge amount of time, and if you don't arrive very early to wait for a good spot, you won't be able to see over everyone else's heads anyway. Plus, ride lines are shorter when everyone else is a the parade!
Have fun!