My parents had a book about sex, pregnancy and relationships. The pictures were mostly cold anatomical drawn stuff. I think the riskiest picture was just naked hugging from the waist up. Since I was too young to read, I assume my parents never bothered to hide the book.

It had pictures showing the baby growing inside the womb. So I learned early on that babies come from women. It never occurred to me ask what triggered it, I think I just assumed women chose to do it or something. It wasn't until 4th grade that I had a proper class about reproduction at school and learned the man's involvement.