I regularly attend two folk clubs and I like both of them for different reasons. However in regard to the thread, one of them is very thin on the ground with under 18's and the other (on average) has about 20-30% under 18.
Why the big difference? Personally I think it is the attitude of those running the clubs? The one with a broad view of what constitutes folk music has the greater number of young people. The one that has a leadership with a penchant for hill walking, itchy knitwear and pronouncing America as Amerikay in songshas an older membership.
As I say I like them both but the second one will clearly fade rather than thrive in the course of time.