J.T.
I'm apologizing now because I wrote you a novel, but I've got lots of info for you!
First of all go to www.tsa.gov click on For Travelers at top and then about the middle of the page click on list of prohibited items, this will give you all the info you need for what you can and cannot take on the plane and what procedures to take with formula/breastmilk for you youngest. Strollers can be gate checked, so keep your kids in the stroller until right before you get on the plane. They will check it at the gate, and give it back to you at your arrival gate. Also if you are taking a car seat make sure on your car seat that it says its aiplane safe some are not allowed on the plane, the ones that are allowed you can take right on and use in the plane seat. Might work well for your 7month old. Its just very awkward to carry through the airport!
I went to Fl when my 4yr old was 8 months and she was great on the plane, I was surprised. But definitley make sure you have some snacks (goldfish, crackers, fruit snacks), a bottle or pacifier for the little one for his ears! If your 3 yr old likes to color definitely take on some color wonder books, they won't be messy and he can go to town coloring. A portable DVD player would also be good if you have one. I would pack a home made "fun pack" for your 3 yr old but don't even show him until you take off and you're in the air to make the most of it! You could get some Disney stuff to get him excited for the destination! Double check the list of things you can carry on, but maybe some Disney fruit snacks, a Peez with a Disney character, disney color wonder book, maybe some Disney reading books, you may be able to find a travel book for Disney that shows a lot of pictures of Disney world to get him into your trip! If you go to the store you'll probably be able to get a whole bunch of ideas for a disney themed fun pack!
As for your actual trip to Disney, it sounds crazy and sometimes its hard to pass everything, but when you get to the park, go straight to the back and work forward. Many travel agencies will recommend this, the lines are usually shorter and a lot of the kids rides are towards the back. Go to the park when they open always quieter right away, most families sleep in a little and go to breakfast. Also, I remember reading this when I went there on my honeymoon, when there are multiple lines for a ride or to get into the park go to the left, its natural for most to automatically go to the right line and for some reason 90% of the time the left line is shorter even if they look the same. It worked for us. and if you didn't get the fast pass look into it, we had it and it was so great. You can scan it at a busy ride and it will give you a ticket for a time frame to come back to that ride and you get to go right up to the front. Sometimes you have to wait a ride or two, but its no where near the full wait time. Be careful though when we were there you couldn't just go around collecting fast pass tickets you can only have so many at a time or something, check in to the details. i think that they have a sign outside each fast pass ride that will say the fast pass time frame. You don't want to get a pass for a much later time frame, because then you will be unable to get a fast pass for another ride until after you use your first pass. Definitely have to go to a character breakfast they're all the time and so much fun. Don't be surprised if your 3 yr old is totally freaked out by the characters, just don't force him to approach them and he'll adjust. If you have a video camera that takes tapes or a regular camera with film, pack plenty because they are ridiculously expensive in the park! Oh and pack batteries you may need for your camera or toys bought another expensive item. Also pack juice boxes or something because the drinks too are pricey and your little ones will get thirsty in the heat. I'm not sure if it is the same all the time, but both times we went in July and August, it rained every afternoon for like a half an hour, it was almost predictable it was at the same time every day and I want to say it was around 3:00pm. So prepare for that if it is the rainy season there now, you'll be able to see the clouds rolling in and like i said its quick but it pours. Good time to see a show or head back to the hotel for naps. But it cools off real nice after the rain. If you rent a stroller at Disney World, you can leave the Disney stroller at one train station, take your belongings and your nametag for the stroller, and then get a new stroller at the next station. If you go to multiple parks in one day, and rent a stroller, you can take your belongings and the nametag from the stroller, show it at the next park, and be given a stroller. Only bad part of the renting a stroller is that it can't leave the park, so you need to carry sleeping children and all your stuff back to hotel. Florida tap water is yucky taste, so plan to buy some bottled water or take flavor packets like crystal light or propel so you don't taste the yuck! Ok I think that is all I can think of, sorry its so long, but wanted to help as much as i could. I can tell you one thing that I remember my mom doing when I first went to Disney as a kid. i was about 5yrs and my brother was 2yrs. On the morning after we got there my mom left a note outside the hotel door with a big sticker of Mickey on it and it was written as if it was from Mickey welcoming us to the park and saying that we should come visit him while we're there. I remember as a kid that was the coolest thing ever like Santa Claus sending a special letter. Hope this was all helpful and enjoy every moment it can seem overwhelming but its the greatest place on earth, truely! Oh and Epcot is nice, but no where near as child friendly as Magic Kingdom. And if you are doing the other parks the Animal Kingdom is great and kid friendly and MGM studios is cool but again more for adults. Don't plan large amounts of time in Epcot and MGM since its your 3 yr old that is going to have the greatest experience! Good Luck and have fun. Jennifer