I'm all for explaining it. Nothing wrong with it. There is nothing perverse about it either. It's a natural thing. I grew up in Germany and they teach sexual education in 6th grade, no opting out either. They don't even teach the biological aspect, but also the importance of a relationship. As a result the pregnancy rate is much lower then in other nations that don't do it. I didn't have protected sex until I was 19. Late for some but it was my choice, and I'm still married to the same man. Anyway I rather have a child that does know those things, then one the doesn't and get into trouble. I rather have them understand and learn it correctly, then from some friends/bodies that are clueless. So the boys had fun with the camera watching chicken doing what is natural. I actually find it funny. Reality is they know the difference, and that is includes human differences. All that tells me it is time to educate the boys. Just be open about it and answer questions. I would not hide the truth. We have a silly joke in Germany about two dogs doing it in the middle of the street. A little girl asks her embarrassed mother what they are doing. She told the girl that on dog was blind and the other one was pushing it across the street.