Let your little ones set the pace. If they want to spend 1/2 hour playing at the Imagination Leap Fountains, let them. Let your kids decide what they want to do....... talk about some of the rides before your trip and let them pick out some "must-dos". If they want to skip a ride, not see a character, that's fine....don't push them.
Make sure they have plenty of rest, drink and food. My parents still tell the funny story of how at our first visit to WDW they had just purchased me Mouse Ears and insisted on taking my picture in them. But, I was very hungry and getting cranky. But my Dad made me stand for this picture so I have the maddest expression on my face in it! OK, it's funny 30 odd years later but I know it would have been a better time for all had they let me get a snack first! :lol:
And as others have said, I cannot stress enough taking a mid-day break for a swim and rest. Plan on being away from the parks for a minimum of 3-4 hrs. Don't burn the candle at both ends or you will all be miserable. Also, schedule "down" days during your trip, when you have no parks or activities planned. Use that time to sleep in, go to the pool, whatever you all feel like.
With kids that age, I would start at Fantasyland in MK. Get to the park at opening, or have a character meal at Crystal Palace before the park opens. (Pooh and friends)That way, when you are done eating, you can stroll right through the Castle and to the rides. If you time it right, the park will just have opened and you will be ahead of the crowd. We did this last April and had only a few minute wait for Dumbo, Pooh, and Peter Pan! We also walked right onto Small World. Plus, we got some great pictures in front of the Castle with no crowd in the photo, just us.
After Fantasyland, go to Mickey's Toontown Fair.....lots of fun things for little ones here.
If you go to AK, don't rush through the Oasis in the morning....there are cast members walking around with small animals in cases for the kids to see if you pay attention....my kids both loved this. Also, in the Pang Trail there is a building you go in before the bird aviary (where the naked mole rats are). There are a lot of interactive things to do in here and the cast members are fun to talk to. If you eat at Pizzafari, there are "back" rooms away from the registers that are usually not crowded.
Have a great time! :wave: