I second the idea of taking them to ALL the parks. We went twice in the last year or so with girls (almost 5 NOW and 2 1/2 now).
MK and AK are more obvious with kids stuff, but like the FP said, EPCOT was their second favorite park after MK as well. We really did our research with EPCOT and my DD almost chose to go back to EPCOT our last day instead of MK!!! The world showcase was great!! She did all the Kidcot stations and thought that was cool (a couple of the CM wrote her name in the their language on the mask she made and it makes an excellent souvenir from her younger days). They love the toy store in England where the Pooh characters hang out (we saw Mary Poppins there once too), in Morocco they wrote her name and the word "Princess" on her mask and as we toured around most of the CMs called her Princess Aubrey which was cool!! Plus, you can find Aladdin and Jasmin in the area quite often. In France, we had usually skipped the movie there (I can't remember what's it called) but we went ahead in as they were starting a show and we all actually found it pretty good and just a nice relaxing family time. Belle and Aurora were also found there.
In Japan we made sure to be at Myuki's (the candy lady's) stand 15 minutes ahead of time and ended up with these handmade candy. It's amazing to watch and a highlight of our trip.
In the American Pavilion we love to watch the accapella group in there (is it Voices of Liberty or something?) DD got pulled from the crowd and sang to and we like the show in there.
In Italy, they have the very entertaining mime/juggler/comedian that we watched and DDs loved! In Germany they like the train setup and the German toy shop. In China they loved the Acrobats and saw Mulan and Mushu and she chose a beautiful chinese umbrella that they wrote her name on for a souvenir.
She loved Rio Del Tiempo ride in Mexico and Maelstrom ride in Norway and she always have to try on the Viking hats they have there.
In future world she LOVED Soarin' and rode it 4 times in one day (twice with each me and DH). We took DD2 on The Land ride which is right next to Soarin' and she loved that (especially the Mickey shaped pumpkins). They also love Imagination with Figment, Turtle Talk with Crush (a MUST SEE!!!), and that's just the stuff off the top of my head.
We finished off the day with Le Cellier and you can tell what DD2 though of it!
As you can tell, we all loved it and it proved to be one of our best days there.
As far as MGM goes, we went there our first full day and spent the entire day there without any problem. They loved Playhouse Disney, Voyage of the Little Mermaid, The Tribute to Walt Disney walk through and movie, The Great Movie Ride (can be scary for some kids), The Muppet Movie, Lights Motor Action!, The Stars and Motor Cars Parade. They also saw a bunch of characters including Tigger, Chicken Little, Abby Mallard, Buzz Lightyear, Woody and Jessie. DD loved sitting on Herbie for a picture.
And don't forget Fantasmic! We all loved it. Since it was January when we were there last, we only had to come in about 30 minutes ahead of time and got a good seat. Both the girls loved this!!!
As you can tell, they had a blast at both parks. Like another poster said, just do your homework before hand and don't miss the small stuff that can be sooo fun!!!! We had the best family vacation in January because I did research and knew what to expect!!! Have a great day!