SLOW IT DOWN - Definitely take it slow..it might be your first time but don't make it your last...when you are with kids sometimes you need to let them be the guides.
STAND IN A LINE - Be prepared to stand in line..doesn't matter when you go you will stand in some sort of line. So bring things to do in line - playing ISPY works good or guess who I am (like charades but you give hints to a character and everyone guesses who you are)
LET THEM BE APART OF THE PLANNING - Depending on the ages of the children let them pack their own suitcase or backpack for the park. My girls like to pack their own carryon for the airplane and they like to bring their own backpack to the park. This year I'm getting the Disney for Kids by Kids book for my seven year old so she can pick what rides she wants to go on. Plus there's a spot for notes in the back.
CAMERA - Bring a disposable camera for them to take pictures! It's great to see their prospective on Disney.
DISNEY DOLLARS - can be purchased at any
Disney store or converted at the park. Great way to teach money and math! My kids get $100 to use the entire trip, sounds like a lot, but every time they ask for something (doll) they have to take it out of their wallet and pay for it. Makes them aware of money and what they really want. Plus it stops them from asking you for money every time.
SCHEDULES - I would definitely throw all schedules to the wind. My kids always nap during the day at the parks, but never nap at home. At home my kids go to bed at exactly 9pm, at the parks I've seen them up at midnight and still full of energy.
REMEMBER YOU ARE ON VACATION - tempers seem to rise when loving families get together for long amounts of time. There's nothing like seeing a parent with their children telling them, "We're all going to have a good time, darn it, so shut up and enjoy it!" This is Disney take things in your stride. If you missed a show there's another one again. If someone dropped their icecream, get another, no big deal. Just enjoy and don't sweat the small stuff.