It's hard. I think we've generally gone with the simplest HONEST answers that seem to satisfy what she wants to know-- and why she wants to know.
Generally I casually buy myself a deep breath and a frantic thirty seconds of deliberation by asking, "hmm... why do you ask about that?" (or something similar) My heart may be in my throat, but I am really good at playing it cool... have to be, because kids sense "things mom does NOT want to talk about" and either respect the boundary too well-- or leap in where angels fear to tread with a certain unholy fervor for finding what will make you turn PUCE in public, KWIM?
If she comes back with "well, I saw these neat pictures of a baby inside it's mom on the bus the other day" then I know that she is asking because of something specific that she saw. If on the other hand, she is asking because she heard the word "abortion" on the news amidst a story of a clinic firebombing, well, that's a different conversation.
In the first case, she's just curious about what the word means-- what does it have to do with babies. In that case, I'd probably go with an explanation which is medically oriented and probably leans a little toward "life-of-the-mother" and "severe congenital deformity." In the latter, I'd talk about what makes people angry enough to do things that are violent in order to make their point.
Different questions, though.
And yes, I've had both of those conversations with my DD-- before she was 8, in fact. I also got to explain what "rape" was to my then-5-yo when she read it on a helpline sticker on the back of a bathroom stall at the Uni where I was working. "Being forced to have sex when you don't want to" was fine as an explanation, by the way-- and it led to a good conversation about giving others permission or not to touch you or do other things to you. Boundaries, that kind of thing. So all in all, while it's not a topic I'd have chosen, it was fine as the basis of an age-and-development-appropriate conversation.
