As you may know, Abby and Lizzy are completely ignorant of "how babies are made"; although they grok how babies get out of a mama's tummy, they've never asked how babies get in.
And thankfully, the four-year-old Lizzy-appropriate explanation (Abby's outside playing) was met with utter disbelief and the assumption that Daddy was teasing "because he's a teaser". Apparently "a boy plants a seed in a mama's tummy," was so outlandish that she simply cannot fathom that it's true (as far as it goes). I can cope with that for now.
And it did make me wonder about the phrase "the birds and the bees". I mean, really, who cares how birds do it or bees do it? It's not how humans (or most other mammals for that matter) do it, so how is it even related? Even the botanical "plants a seed" reference above is more accurate.
So I looked it up, 'cause that's how I roll. And while I realize that Wikipedia is not a be-all and end-all source, it does make sense, in a Victorian "it's my bosom and I never mention it" sort of way (yes that is a reference from my favorite Heinlein novel; you see, the heroes are visiting Oz and... never mind).
Anyway, Abby came in after the subject had been dropped but I'm pretty sure it won't be long before she asks for more details too. And I'll tell her.
But I'm not looking forward to the conversation.