guest I am missing something. When you say that "most of the lyrics are not appropriate for a kid to sing" what are some of the songs you are thinking of specifically?
I am hard-pressed to think of any bluegrass songs with lyrics that I would call objectionable.
But anyway, How about
Foggy mountain top
Bringing Mary Home
Ain't gonna work tomorrow
Hello stranger
Let the whole world talk
Kentucky
Blue moon of Kentucky
etc.