The Music Man is always my first choice when thinking of a show that is kid-friendly, but not intended to just be a children's show.
Also, my brother just got cast as Big Jule in his 8th grade production of Guys and Dolls, so maybe that one as well?
The Sound of Music could work, too, especially if they're learning about WW2 in Social Studies class.
https://newplayexchange.org/users/99643/amanda-delalla