Don't force them, they'll just resent you for it and be less likely to respect your musical preference.
You should, however, introduce the style to them. There's a great band called the "Pickin' On Series," which is a group of terrific bluegrass musicians that do covers of popular songs you're kids might like, but in bluegrass style. It might get your kids headed on the right path.
15 year old bluegrass aficionado.