Where would today's kids see Dumbo, exactly? Unless the parents happen to have the DVD, which I doubt the average American family does, they wouldn't. Toon Disney is no more and the only animated films that Disney Channel or ABC Family play any more are Pixar films. They used to play the animated features when we were kids, but not any more. You are lucky to even see Aladdin any more. I don't remember the last time anything like The Lion King or The Little Mermaid was shown on tv. So I would guess most kids HAVEN'T seen Dumbo. I know we don't own it.
I'm sure kids know who dumbo is from the hard-cover Disney kids books we all know and love, but I doubt most kids have seen the film.