Imagine when son grows up and he knows his parents are into cuckolding. Moreover his parents never hide it from him making it as a part of family life but they always aware him not to tell everybody about that. This way son always had quite open dialogue with mom about sex, relations, girls etc. So one day as a part of education they both (but mommy at first I guess) feels that time has come and make a family decision to take their son to the sex/swinger club with them.

I think it could be possible, tho. This is a wide world.