Personally I don't think ANY workplace - big or small - has the right to ask what your intentions are for another child. And you certainly shouldn't feel under any obligation to tell them. I understood your comment that they're not being mean or negative ... but still. Why ask you? If you have another baby, presumably they'd have approx 5-6 months notice to plan and budget.

And while their questions could be to do with budgeting, but it wouldn't be unheard of for a company to deny a woman a workplace opportunity (be it a position upgrade or further training) because she's either pregnant or planning children. I'm not suggesting your company would do this to you, but it certainly does happen. Trust me.
100% right, AndiE, NO workplace has any right to ask you this! It is illegal and should you answer it, and then subsequently be fired, made redundant, or be overlooked for promotion, then you would have grounds for a discrimination suit. Perhaps let the person know all this and then say "so now do you STILL want to know???".

At the very least, make a note of the conversation in your diary so just in case anything ever does come up at a later date you can refer back to it. You would be surprised how often it comes up, and more often than not in small companies! And as AndiE also said, they'll already have around 5-6mths to plan for it, that is more than enough!

You could always say: When I have a spare few thousand dollars, I'll take an awful lot of drugs that make me feel nauseous, bloated and generally feral for about three weeks, then have some surgery, then DH will toss off into a specimen jar, which will be mixed with my eggs in a petri dish, and then hopefully, if the universe decides it's time, we might get the chance to have another baby.

Or.... You mean you're asking when DH and I will be having sex again? Isn't that a little bit personal? It's not like I want to know when you and your DW are going to shag....
Love it!!!