We took DD (now 6 1/2) for the first time at 1 1/2 years old. Really, at that age, everything made her eyes light up. It was great.
Her favorites were: the furry characters, the birds, Dumbo and the Carrousel.
Oddly enough she wasn't crazy over any of the face characters. I don't think she liked 'strangers' talking to her. Other than that she enjoyed whatever we enjoyed.
Pooh's Playground in Fantasyland wasn't open back then, but if it had been I know she would have LOVED that, especially the pop jet fountains.
We took her again at just over 2 years old, and by then she was more familiar with the princesses and liked them better. She was awestruck by Cinderella at CRT breakfast. She still loved Dumbo and the Carrousel, and of course the furry characters, but thankfully by then she was outgrowing her fascination with the birds, lol.
We bought her a Minnie Mouse dress that trip and she wouldn't take it off. Really, she wore that dress almost every day from the time we bought it until we came home. I think I only got her to take it off one day, so I could wash it. It's funny to look back at the photos from that trip... there's a Cinderella dress, one shorts outift, and all the other photos are in the Minnie dress. It looks like we were only there for three days, lol.