We just did a Disneyland trip (not Disneyworld) with an almost 2yo, 4yo, and 6yo. We have also taken a trip with my stepkids, a 10yo and 12yo a few years back.
The first trip with the older kids we were on a strict budget. Our hotel was across the street from IHOP and they had a buy an adult meal, kids eat free promotion which we used a lot. I was SICK of IHOP by the end of the trip! We also bought some snacks in the park, and it actually was worth it. The giant turkey legs are worth it, the kids split one and were happy. We also ate those frozen bananas, which not only were yummy and semi-healthy, but soothing on a hot day. We did take along a lot of snacks which we packed from home...or if you can find a grocery, buy them when you get there. Examples: beef jerky, cheese sticks, cereal snacks, cheese-n-cracker packs, pretzels, etc. I didn't take enough on that trip, but it helped and YES, they will check your backpack upon entering the park but have never said anything to me about the food I bring (I don't pack it to the gills but it's obvious I am bringing food). I asked the gal who was checking about it this last time - she said they are checking for things like firearms and glass bottles - no glass allowed!
On that trip, we were horrified by the cost of a drink in the park. At $2-4 a pop, you can go broke quickly. We tried to bring and use refillable water bottles, but we hated the taste of tap water. It's very minerally in California (might not be so in Florida).
So, on our second trip, I brought along a water bottle for everyone. I also brought a BUNCH of those single serving powdered drink mixes (Crystal Light or you can buy the generic brand at Walmart). This was the BEST idea ever! We all drank much more and stayed hydrated, we could mix it up as we went, and even the baby loved the taste! And there was no cost to us for buying overpriced coke or junk food drinks in the park!
We normally pack milk and bring cereal when we travel for a fast, cheap breakfast in the hotel room. This time it was not possible. I do know that at Disneyworld it is very hard to get to the outlying area if you don't have a car (it is so large). If you have a car, go find that stuff and keep the milk in the fridge. It makes less stress getting everyone into and out of as few restaurants as possible!
As for rides, just take it easy and slow. We did split up a bit - for example, one night my husband took the 6yo out for the fireworks and extra rides, and I stayed home at the hotel. It was really nice to get the extra rest and the youngest two were tired as well. For the most part, we stayed together and everyone learned to take turns. The nice thing about Disney is that there's always somewhere to sit, always something to watch, and I didn't mind waiting around nearly as much as I thought I would! And the rides seem to appeal to all ages. The 12yo actually loved Dumbo! Which cracked us up. But once I got on it, I understood.
We did have parkhoppers, but did only one park per day. In Disneyworld, I think the layout is larger, so definitely don't overdo it! You will be walking a LOT. We did have a list of MUST see things, and then some which were not so important and could be skipped. Since we were there in December, we had been told to expect long lines - but it was not that way all over. Some of the rides that I wanted to go on like Small World were decorated for the holidays and the line was huge. We skipped it. We definitely wanted to go on the Haunted Mansion, though, so we got a FastPass for that one. The one that was toughest to get on as far as lines go was Finding Nemo. We had one early in the park day and used that time to get in line immediately. It only took about 15 minute wait that way. It was not a ride that I loved, but for the little ones - they did enjoy it. It was important to them and we fit it in that way so it was least hassle all the way around.
We rented one of their strollers, it was more than adequate - and we got to avoid the hassle of taking our own stroller on the airplane. And we got the multi-day pass for it to avoid standing in line to pay each time. We made it thru the airport ok, just took longer as we let the littest one walk a lot.
I was having foot problems and we rode on a lot more transportation in the park than we normally would have. It was very fun, actually! We took the train, fire truck, and horse-drawn carriage, and it was one of those magical things that turned out to be a great memory.
I packed a bag of busy toys and some diversional things for the plane trip. Coloring books and the triangular crayons that don't roll...the coloring pads that have the invisible writing that comes out with the special pen...etc. We also had gum and small lollipops in case the plane ride affected their ears. I packed the kids' handheld games (leapster) and invested in earplugs so they didn't bug the other passengers.
Have FUN!