I was poised in front of the fireplace, firelighters and matches ready, when Brian appeared.

"Can nuns have babies?" and we're off.

I'm on a loser from the start. "Yes, well, technically, but nuns don't get married, you see." "So, are you supposed to be married to have a baby, then?"

"Of course not," I reply. "Sean's mammy isn't married."

"Well, why don't nuns have babies then?"

"They take a vow not to" is the best I can do.

"Could anyone make a vow like that?" (Why would they want to? I wonder to myself - no disrespect, sisters.) "Like Auntie Helena? She has no babies and she's married." (No, Brian, that's called the Pill.) I explain that Helena will probably have babies some time, and am tempted to add that she's probably having great fun practising!

We proceed. "Why does Ciaran look like you, and everyone says I look like Daddy? How can you look like the daddy when you come from the mammy's tummy?"

"Well, the dad plays a part in all this too, a very important part."

"But he does nothing and the baby ends up looking like him. Weird!" You can sing it, Brian.

By now the colour rising up along my neck is in direct competition with the pins and needles in my legs from teetering in front of the fire. "When a man loves a woman . . ." is eclipsed by the next conundrum.

"I saw something on the TV where someone's father died before they were even born. Is that not impossible? And what if someone says they don't know who the father of the baby is - but they must know!"

Oh, why are fathers so problematic? There's a lot of to be said for those species that procreate by splitting cells. It's the cells coming together that cause all the problems.

I consider my options: buy a book; spill the beans on the whole process here and now or else topple over on my haunches and hope all is forgotten in the melee. Or perhaps I should get his father to take over, seeing as he's the issue here.

Roll on sex-ed in primary schools - aren't teachers born communicators, anyway?

In the end, I reach a kind of compromise. "Brian, I want to finish lighting this fire, but we'll sit down later and I'll explain it all to you, I promise." What am I facing? Brian turns around and grins at me.

"So, I'll tell Ciaran we're off to McDonalds, then," he says knowingly. Yes, I've been set up. No matter how I handled the barrage of questions, the punchline would have been the same. And, I'll wager this boyo knows more about going forth and multiplying than he's letting on.

Maybe I'll settle for buying him a book after all. Let him work at finding out about these things - and it'll cost me less than fast food, too.