I love how in-character they can be. A couple experiences we had that were fun:
My youngest was 3 at the time and she couldn't go on the rides she wanted to because she was too short, so I ended up taking her to all the characters. When she saw the evil stepsisters and Lady Tremaine, she pulled me into the line. I don't think she realized they were villains until she got to the front of the line, because by then she was a little scared, but she tried to be brave! Anastasia and Drizella were funny and overly sweet, complimenting her on her nice hair and outfit, when it was obvious to the adults that they were really acting jealous of her, so they stayed perfectly in character while making her feel welcome.
When we met Mr. Incredible and Frozone, Mr. Incredible put on a little show for our video camera, dashing this way and that to see if my husband could keep up. Then, when he was backing up, her ran into Frozone. They both got into a play "fight", puffing out their chests in a kind of "you want a piece of me?" way. Complete bravado.
When we met Anna, she wanted to play hide and seek with the kids. So she made them cover their eyes and count to ten while she stepped two spaces behind her and hid behind the curtain there. I'm sure she does that with a lot of kids but it just made me think how the real Anna would TOTALLY do that!
Once we were at Akershus and when they do that little parade, Aurora took my daughter's hand and led her around, then talked to her for a while. A few days later we were waiting for Impressiones de France and a woman told us that Aurora and Belle were meeting there and would we like to meet them? Well of course my daughter insisted, so we went over there, and it was the same Aurora. She remembered my youngest and even brought up things they'd talked about before. Which I have to say, was AWESOME luck!