If your child's school doesn't already do something like this, it may be worth the effort to talk to the school administrator or teacher to see if one can be started. If the school you're involved with isn't already part of an association, perhaps area schools could be contacted and a representative from each school could meet to organize this annual event. One of the schools would have to host the event, and things like fees would have to be discussed. College professors make great conductor choices. They are the ones who help choose the song selections. Then, all the schools purchase their own copies for the students to use.
The students are definitely stretched with their musical knowledge and performance skills. It is such a fun and educational day for them. As a new director, I'm learning a lot from the guest conductors as well.
Let me know if you're interested in something like this. I'd be glad to give you more tips on how to start a Music Festival in your area.