If you have small kids, who are a little timid of the dark, one of the things they don't tell you that almost all of the rides, including the Pooh Ride, are dark inside. We take a small pen light flashlight. Seems to work well--calms the fears of the little ones without disturbing other guests. Take spare batteries for it to. Those
AAA batteries are hard to find and I guarentee it will get left "on" sometime...
Even though our daughter is out of diapers, we pack a package of wipes and take the "travel container" for them into the parks each day--and then just refill at night. There is always something or someone sticky, dirty, greasy, sweaty.....
Take ziplocks---and put any liquids you are taking (shampoo, hair gel, contact lens solution, suntain lotion, etc.) in zip locks prior to putting them in your suitcase. Trust me on this one, voice of experience here....
If you can get up and get going in the morning, try and get to a park when it opens--especially MK. If you have small children, head straight to Fantasyland. Little ones have no patience when it comes to waiting in lines. You can get a lot done in the first hour or two.
Wear good walking shoes/tennis shoes---every member of the family! You will put more miles in a day than most people are used to. I love the Thloro socks. Made for runners (which I am not!) but seem to be very cushiony and provide support. They are expensive, but well worth the $.
Let the kids run in the fountains at Epcot (and at DD)---heck, the adults can too. Plan ahead and take a spare change of clothes/shoes. Nothing worse than listening to parents scream at kids to "GET OUT OF THAT WATER RIGHT NOW!!" on vacation. The first time our daughter did this she was 2 1/2 (she played it for nearly 2 hours straight); and she still talks about it to this day.
Magic is all around you--you just have to slow down to see it. We have found characters in quiet corners, sat and watched very entertaining street performers, and have had magical things occur--but none of it would have happened if we did the commando raid of the parks. I am sure you will enjoy yourself--and if you have anymore questions, just ask.
Trudy