The previous poster gave you great advice.
AK is REALLY HOT. We were there in May, and it was tough - I can't imagine it now. Maybe just plan a morning there. We used some little personal fans I found at
WalMart..they had a foam fan which didn't hurt if the boys put their fingers in it - and it also sprayed water. They were really handy.
We took our twin boys to WDW for the first time when they were 2 1/2. One was afraid of all the 3-D movies, but the other LOVED them. So - be prepared that one of you may have to take one of the kiddos out on a few attractions if they are frightened.
At 2 1/2 our boys loved Pooh's ride - really all the rides in Fantasyland (we skipped Snow White's Adventure because we thought it would be too scary for them). They got a real kick out of the play area across from Pooh's ride as well. Keep in mind there is water involved in the play area, so bring a change of clothing, socks and shoes. They also were fascinated by Spectromagic...when they saw Mickey standing on that first float, with all of those lights, both of their mouths dropped open in amazement and they both said "Mickey" very softly. Toon Town was a big hit as well. They LOVED Cosmic Rays for lunch, as the other poster mentioned. They danced in their seats throughout our meal while we listened to the "alien dj". Also, the chicken there is really good. At AK, their favorite was Triceratop Spin, but they also enjoyed Kilamanjaro Safari. At MGM, Playhouse Disney was a favorite, of course. I don't think we did much at EPCOT when they were that age. Oh - and the bus ride to the parks was as much fun for them as the rides in the parks themselves.
Both of mine were a little leary of the characters at first, but toward the end of the trip they really warmed up to them. That year, we did Crystal Palace (which they still love at age 4), Garden Grill in EPCOT (food wasn't as good when we went this year), Liberty Tree Tavern (they loved Pluto and Chip n Dale - plus the food is excellent).
I brought snacks and small juice boxes into the parks with us each day...usually teddy grahams or goldfish because they were easy to pack. Keep in mind that AK does not allow straws - I brought some of those take n toss sippy cups to use at AK. Also, remember that the counter service restaurants will give you free water with ice in a cup if you ask for it. On hot days, that's a big relief.
We tried to stick to their normal sleeping schedule as much as possible (with the exception of the night we did the Spectromagic Parade, which caused us to get to bed later than usual). This helped to keep tantrums at bay, for the most part.
Have lots of fun! You'll really enjoy the sense of magic you'll get watching THEIR reactions to everything they see. Also, we found our kiddos' language expanded and they started talking more after our trip. I guess they had a lot more to say after their experience!
Tip - I brought along some of those "table toppers" to put under their food in the counter service restaurants. The tables aren't always the cleanest, plus you don't have to get an extra plate - you can feed the kids off the table toppers. You can find them at Babies R Us or Target. I also brought along some Disney stickers I found at the dollar store...this way they had something to play with while we waited for our food in the restaurants.
Another tip - If your kids aren't potty trained yet, the Baby Centers are usually cleaner than the other restrooms for changing the kids' diapers. They also carry baby supplies in case you need to purchase something you've forgotten.