On the kids noticing animals mating:
Last week, I took the kids to the zoo. When we were watching the lions, the male decided to mount and mate with the female. I could see what was going to happen, in that moment I decided precisely how to react. I could have dragged the kids away quickly, and they wouldn't have seen a thing. I could have just said that the female was giving the male a "piggyback ride". Instead I decided that I should treat it like no big deal. I answered their questions in the moment, and the subject hasn't come up since then. I want my kids to know that they can ask me anything. I don't want them to be afraid to ask a question because I shrug that subject off with discomfort.
I have a big problem with parents making sex out to be unclean, something to be ashamed of, or taboo. Should sex be a private matter? Absolutely, sex is a private matter between the two parties involved. Society wants to make sex and sexuality out to be a public sport rather than a private relationship function. That doesn't mean that we should shut down all conversation/questions regarding sex and sexuality. Instead, we need to teach our children that sex is a private matter but not something that is shameful. Those lions had sex in front of my kids. I think the college students that saw our kids witness the lions having sex were more disturbed about it than the kids were. Those college students were embarrassed, my kids moved on to looking at the hippos soon afterward.