I can say, that my mother never discussed sex, as such with me. What I ended up knowing, prior to reading books, came from other kids, who were full of adventure and information.
Relative to abnormal sex, my mother told me about what to report to her about any abnormal acitivites. As a matter of fact, once when I was a kid growing up in the inner city, a man rode by my car, where I was seated and exposed himself to me. I reported this to my mother and she told the police.
In my neighborhood, we had an old guy, the kids called "Mr Pinch". Everytime, we kids got near him, he would pinch our butts. So we made it a point of running when we saw him and yelling "Pinch Man" is out.
Kids know what's normal and what's abnormal They don't need a PhD in biology to know that many acts are abnormal and shouldn't be indulged in.