Nate knows that the girls have an egg, and the boys have a seed, and never once has he thought to be curious about how those jive cats get together in the first place. I was expecting it at 3, and at 4, and had finally quit expecting it when I was blindsided driving to a Chinese banquet a few Fridays ago.
I'm making a thing out of it, but in truth the question was uttered quite simply, and telling him was far less of a thing than I had expected it would be. He already knew that boys have a penis, and girls a vagina (which I've explained as an inside-out penis, a tunnel kinda-like), so I just explained the obvious points and that was that. I think I remember saying something about "rubbing against" and the seed coming out but it is kind of a blur.
He was totally non-plussed. He thought about it for a while, and then asked "So you did that?" and I said "yup!" and he said "With Daddy?" and I said "yup!" and we kept on driving. He thought again for a while, and then asked what was clearly most confusing him: "How do you know when to do it?" After resisiting saying "Oh you'll know" I explained that when you were older, mostly grown-up, and had a girlfriend or a wife or a boyfriend or a husband, you'd talk about it and decide you were both ready to do it. That it felt good and was fun, and a thing that people loved did together - sometimes to have a baby and sometimes not. He was still worried about knowing when to do it, I have this picture that he's worried he's going to be at school and all of a sudden it'll just be happening to him and how weird would that be? So I put it in a bit of context by saying that it would be around when he started driving that he'd start to think about doing it, that he didn't need to think about it until then, and that seemed to reassure him.
All in all, it went swimmingly. He hasn't asked about it since or brought it up in strange company or told his friends all about it, so that's lovely. A lovely boy, my Natey.