My two cents' worth:
(1) Leave the young people alone.
Why? Because when adults interfere with kids, they always suspect an
ulterior motive, and they're not stupid: we want them to subsidize our
classical music habit. It isn't going to happen because we urge them
to do so.
(2) Keep listening to classical music.
(3) There's no harm if young folks happen to notice that we're listening
to classical music regardless of their presence in the area.
They resent being bombarded with classical music as if it were some
musical propaganda. On the other hand, if they stumble on you quietly
listening to your favorites, there's usually a question about what it
is, and more often, who's playing. (In popular music, the performer is
more important than the composer.)
Unfortunately, there seems to be no pattern in youth behavior. A
generation ago, young folk seem to come to an age at which the more
intelligent ones instinctively turned to classical music, at which point,
of course, there were a lot of inexpensive LPs/CDs they could buy (around
1970-1990). Whether the present generation of teenies will arrive at
this stage remains to be seen. If they do, we may be forced to bootleg
copies of our precious own CDs for them.
I have little doubt that my words will have no effect on die-hard
proselytizers; but kids of today are more convinced of the value of
their own music than we think. Most of all, they can dance to it...