DS4 was 2 1/2 for his first trip and he did great. It was also his first time flying (2 hour flight) and there were no issues. We had toys and coloring books to keep him occupied on the flight there, and on the way home he was so tired after a week at WDW, he fell asleep in the airport and slept most of the flight home.
We went to all four parks and he enjoyed them all. He was a huge Little Einsteins fan at the time so was very excited to meet the characters, and we did a few character meals (Chef Mickey, Garden Grill, and Hollywood & Vine come to mind immediately). He was a little scared in The Garden Grill restaurant at Epcot because of the lightning, but seeing Mickey there helped calm him down and soon they were watching the rotating scenes together. He rode a few rides at MK (Dumbo, It's a Small World, the flying carpets, and the carousel stick out). We alternated early mornings and late bedtimes so we weren't always on the go and even took a day to sleep in, stay at the resort, swim and relax. Some days he napped in the stroller, some days we went back to the room to rest. Overall it was a great trip!