I've never been one to be grossed out at the concept of my parents having sex. I don't understand why other people do. Of course, my mind doesn't go specifically to details so that might be it. It could simply be that my parents were also semi-nudists so lack of clothes seems completely normal.
I don't know if it was because my Mom was German, or that we were living in Germany for most of my young life, but my parents thought it would be a good idea to tell my sister and I where babies came from at an early age.
Or maybe it's because my sister would draw these really interesting stick figures having crazy sex. I don't know where she learned it, I just remember seeing her drawings and then mimicking them. I do remember my mom talking very calmly to us and asking if someone had touched us in that way after she found the drawing books. It wasn't the case, but to this day I really don't know where my big sister got her inspiration.
So around that time my mom and dad sat me down (I assume big sister got her own private sit down) and proceeded to tell me about sex and babies. I was engrossed, I had no idea that stuff like this was real, or this complicated. I asked a lot of questions and my parents handled it like champs. They even told me that when Mommy and Daddy go to bed naked they will probably be having sex and that's why I should knock on the door before coming in.
The conversation wrapped up after I-don't-know-how-long and I skipped off to play with Big Sister. My parents admitted they were bursting with pride at how well my sister and I handled this particular milestone.
The next day my school called and my parents sat me down again to talk about privacy.