We did AK and MGM in one day this past Sept. 29th, with an 8yo and a 2yo. I'll try to remember exactly what we did, so you can see what we had time for:
We arrived at AK around 9:30, grabbed a fastpass for Kilimanjaro Safari, then headed over to Dinoland where there were no lines, so we rode Triceratop Spin, then dh and I took turns on Primeval Whirl with dd8 while the other took dd2 on Triceratop Spin again and played in the Boneyard. Then, dd8 and I rode Dinosaur, and then it was time to go on KS. I really wanted to see FOTLK, but the show times just didn't work out based on our FP return time and the fact that dd8 wanted to be at MGM by 2:00 for Power Rangers autographs. Let's see, we were done with KS around 12:00, so we ate lunch at Tusker House, then headed over to MGM. I would have loved to stay at AK longer and do some exploration trails, but dd8 and dh just aren't that into the place.

So, depending on whether you and your dh want to do some less kiddie-ish things or not, and how into the animals your kids are, you may not have time to do everything you want. I like the idea of going to AK on an EMH morning, though. If you got there before EMH opening, you'd have 1.5 hours more than we did and could easily get a couple more attractions in. You'd probably want to skip ITTBAB anyway, as it can be scary for little ones, and Tarzan Rocks (loud for little ones). The Pocohantas show is really geared towards little kids, though, your kids might like it.
We arrived at MGM around 1:30, grabbed FP's for RnRC, headed over to Streets of America to get Power Rangers autographs. Probably were there till 2:30 or so. Then, went back and got FP's for ToT, baby swapped to ride RnRC, then baby swapped and rode ToT. I took the 2yo to HISTK playground while dh and dd rode ToT and RnRC again. Then, dd2 and I went to see Playhouse Disney while dh and dd8 watched LMA, and by then it was around 7:00, we were tired, ate a quick dinner at ABC Commissary and went back to the hotel.
As you can see, we didn't get much done at all. We tried to make it to Beauty and the Beast, but ToT had a little technical difficulty and by the time dh and dd got out, we'd missed it. That's the one thing I don't like about MGM. Since the majority of the attractions are shows, you have to work around the showtimes. It never seems (to me) like one is starting at a good time to just leave one show and head to another. The next show we want to see is always starting too soon, or far enough out (so we think) to hit one of the thrill rides in between, but then something always seems to get messed up and we end up being too late to make it to the
next showing, too.
Anyway, with the ages of your kids, you might not want to do a whole lot more at MGM than we did, anyway. At age 4, dd was bored stiff on the backlot tour on our previous trip, LMA might be too loud for your kids. Apparently, some little kids think Muppetvision 3D is too scary and VOTLM is too dark, so I don't know if you want to take your kids in those or not. If you don't spend as much time on the thrill rides as we did, you could probably fit in one or two more shows, which may be enough for you.
It all depends on what you want to do. We know we missed a lot at both AK and MGM by doing it this way, but we hit our (well, our kids') favorites, and we were able to schedule a full day at each water park and two full days at MK, which are more appealing to our family than either AK or MGM. You just have to decide where your family wants to spend their time.
Good luck. No matter what you decide, you'll have a blast!