Help! what is the movie where... ? 10 easy points! be quick!?!

Help! what is the movie where... ? 10 easy points! be quick!?

okay, I've been trying to come up with the title for a week now.
I think it's a Disney film, and there's a girl (10 or 12 years old) that has to find her little brother in a kind of "magical kingdom"? I'm not really sure. It's not animated, the girl is real, an actress.
And I keep thinking of a scene where she's on these sort of never ending stairs and her baby brother keeps appearing and dissappearing in them, and I think there's an evil guy making fun of her.
Also, I remember a character that lives in a dump, her/his house is made of garbage.
That's all I can come up with.
I'd apreciate some help.

labrynth