as the male half of a swinging couple, i can say, no, my parents dont know, they probably never will. my dad might give me a high five and be like "good on ya" my mom would freak the hell out, my parents are way too conserative to even WANT to hear anything about my sex life, not even on accident
keep in mind, their reactions arent in any way associated with homophobia, my mother has had many gay and lesbian friends over the years, and my dad doesnt really care one way or the other about gays and lesbians.. they just dont wanna hear about it
now my fiancee on the other hand, her parrents have been swingers for 30 years at least.. we had to tell them, simply to make sure we dont intermingle people that we know, or parties that they are attending will not be attended by us.. that would just be awkward