O.,
You will have a great time, just know it is hot and humid and it rains, but when it rains it is a good time to be at the parks as people usually will go back to their hotels or sit it out somewhere it the park, but we used to our boys that they will not melt and we would make a run for our next attraction. Like the other moms said you can bring your own food in and it would be good to bring water, fruit snacks, nuts anything the kids would like to nibble on and would save you money.
Also Disney restaurants provide a lot of food when you do eat at one, so if the kids are smaller you could more then likely share a meal between two kids and/or some of yours with one smaller child. Also if you can use the buffet places as you get a lot to eat and they are kid friendly and have a lot of children foods, like mac and cheese, chicken nuggets, etc. You can also book a dinner at one, like Hollywood and Vine and then get preferred seating for Fantasmic later that night and not have to wait in line.
The idea of “pre-purchasing” some items at Disney is also a great idea. There is a Disney Outlet not far from WDW (http://www.premiumoutlets.com/outlets/outlet.asp?id=17) and they sell items from the parks much cheaper, it might be last seasons things, but who cares. We went there last year before we checked into our hotel and bought the kids each something so that we would not have to spend more at the parks to get them something. A few years ago when we went I made them each a lanyard before we left and give to them when we got there (and we put the pouches on the end to hold the tickets and Fast Passes). I figured out each of their favorite characters, got them that person on the lanyard and then purchased a mess of pins to put on them, all from e-Bay. Then we limited them to getting one or two at each park. We also gave them each their own Disney Gift Card with I think $25.00 or so on it so they could only spend what they had an no more.
If the kids are small, take advantage of the park that opens early and then take a break during the day and go back to the park that stays open late, that is the advantage of the Hopper Passes. Also use the Fast Pass system, pick an attraction you would like to really do, get a Fast Pass, you have an hour window to use that Fast Pass, before going on that attraction, get another Fast Pass for the next one you want this way you are a step ahead. Only one person has to go to the Fast Passes they just need all the tickets when they go.
When you to the first park, get your photo taken by the Disney Photo people, they will give you a Disney Photo Pass card (kind of like a credit card) and you use it when ever you see a Disney Photo person and have them take your photo. They even use them around the characters. When you get home you can log on and check out the photos and only purchase the ones you what and you can also add borders and dates. Disney has made it official! The ability to pre-purchase Disney's PhotoPass CD for $99.95 has returned and is available to everyone; this will allow you to get every photo that is taken at the park and including the ones that you can “add” by adding borders, dates, etc. http://www.disneyphotopass.com/previsitoffer.aspx
I also have a spreadsheet that I made for my boss when she took her daughter a year ago, I have updated some of it recently for someone and would be happy to send it to you, if you would like it just let me know. We are going in Oct. and Dec. with each of our adult sons, one is in the Coast Guard, right now stationed in the Gulf working on the oil spill and the second is in the Air Force, stationed in Abilene, TX, so for the last couple of months we every pay day we go to the Disney Store and add 25.00 to a Disney Gift Card so when we get there that will be our spending money, we have also been doing it for each of our sons (using their money) so they also will have one to use. Also let me know if you have any other questions as we have driven down many a year.
I am sure you will have a wonderful time!