We took our girls last September, and they were 4.5 and 2.5 at that time. Here are some key things, and some other posters have already hit on them as well:
1. You cannot do Disney Commando style with a 2yo! You need to plan on taking your time, and taking breaks. We would go to the parks early, and stay until just after lunch time. Back to POP for a swim, and then it was nap time. After the nap, we went back to the parks for dinner and some more fun.
2. Bringing a stroller is a must! Umbrella strollers are the best. Remember, if you are using the Disney bus system, you will be lugging this thing around on the bus, so it should be something light and compact. If you rent a stroller, it is left inside the park. With very few exceptions, you are hiking out to the bus stops, so having a stroller is key.
3. If possible, go to the parks after the peak hours. Some have sugested to go during EMH's. If one park is having EMH's ,I would head somewhere else!
4. NAPS are essential. If my girls hadn't napped during our trip, I think we would have had major problems. The one day we didn't nap, was a day we planned on staying at a park straight through (it was closing early due to the
MNSSHP). They were in bed by 7PM!
5. I agree with the buffet and family style restaurants. Your 2 yo can eat free at those places. The character meals were great.
6. Speaking of characters, while my older daughter was OK with all characters, my younger DD had some issues with some of the big (tall )characters. Sully from Monsters INc at MGM, Goofy, and a few others. She was good with all of the face characters. Sully is about 7.5 feet tall , and towered over me!
Some people will tell you that a 2yo won't remember the trip. HOGWASH! My daughter talks about her trip almost every day, and it's been almost a year! Plus, you'll have pictures, and maybe video to remember the trip by as well.
Good luck....and remember.....NAPS rule!