Okay. My cousin remembers this movie about 2 kids who go on an adventure and walk on a sideways sidewalk. Any ideas?

The closest thind to the steps idea I remember is" labrynth"

Except in the Labyrinth, there wasn't 2 kids going together.
The part with the stairs was Sarah trying to go after her step-brother, Toby.
I think it's a different movie, but which one I'm not sure of yet.

Whenever you hear about a "sideways sidewalk", the answer can only ever be... The Hugga Bunch Movie. In France, there are rumors that those who have seen it have been cured of gout and bursitis. It's just that good.

Yep I agree,
Its definatley the hugga bunch.
I still have this movie.