The kids should be in their early 20s at the OLDEST... as in the film. Maybe even only the leads. They ran all the way down to about 8 years old, which would also be historically correct. This is a very "young" show, and I would go with unknowns as the Newsies, and throw in a few reputable stage actors in the adult parts (not "stars" like they did in the film with Duvall and Ann-Margaret). Disney likes to keep "big names" out of their theatre casts (have you noticed?), so it's less of a let-down (both with audiences and at the box office) when a big star leaves the show.
I think this could work on the stage very well, but with some major overhauls in the book, and of course new songs added (they didn't have nearly enough in the movie to fill a theatrical version). But it's worth the effort. I can see the big period street scene set now!
"Jaws is the Citizen Kane of movies."
blocked: logan2, Diamonds3, Hamilton22