I have one family in which I'm teaching a nine-year-old violist, a five-year-old violinist and Mom. Mom's learning some bluegrass fiddle. I suggested that she get a certain book so she and the violist could play together, and she said, "I'd like that, but he insists on only playing classical music. I suppose there are worse things he could be a stickler about."
Ah, how well I remember being a classical-only snob and missing out on a whole lot of music from the '80s. And my parents were more into folk music and light rock. Now I have to listen to classic rock stations to supplement my education.