In the 1951 film, the March Hare and the Mad Hatter's joyous reactions when Alice tells them that she liked their singing. The Mad Hatter even reveals that she's the first person to compliment them (although she quickly finds out why they never get compliments, with the two of them being stark raven mad and all).
This involves an Alice performer at Disneyland, read the first two stories on this page.  (WARNING: the first one contains a Tear Jerker)
In the 2010 film, The scenes with young Alice and her father: "I'm afraid you are. You've gone off your rocker. You're totally bonkers. But I'll tell you a secret: all the best people are."