My mother had been always very frank and open whenever we talked about sex (inspite of her strong religeous education which she tired to pass over to us) and had thus great confidence with her children (2 sons and 2 daughters).
She caught me and my sister enjoying SM plays once (we were 13 and 15).... we came away with a short but hard reprimend.
Some years later she discovered me (24 y.o.) and my then girlfriend (20 y.o.) having contacts with other swinging couples.... other severe reprimend . Now that I am 50 y.o. and my mother is 76 y.o. and we still have a lot of confidence; in order for her to understand certain relational problems in my sentimental life, I had to tell her that I definitely like trasgressive sex, including SM.
She does not share my tastes and my passions, but she accepts them, as far as these belongs to safe and consensual sexual activity..... though we never discuss details.
My sister knows much more, but she had been my first slave many many years ago.
My brother confessed to me some years ago that he is in SM too (as a master) .... he has/had a relation with an american submissive woman (of course they don't meet very often).
Only the youngest sister, who is very religeous and seems very straight, is officially unaware of all this (but I think she has some glimps about me and my tastes).

Generally it is proven that the family (children and parents in a first place) is the place were you seem to find the least understanding for your sexuality. I am happy to say that was not my case.

I must add that my parents were extremely cultivated persons, with a very strong liberal spirit (inspite of being very religeous), we children are agnostic to 75% (3 out of four), but inherited the same unbreakable liberality.

We like to say that we are Liberals, Libertary, Liberistic and a little Libertine

I try to be open and sincere with my own children (daughter 22 and son 17).
I shall not confide private things to them, but I am very honest and sincere when they want to discuss any subject with me ... as a consequence they have a fairly good picture of my quite open sexuality and some suspicion about my taste for BDSM .....