Now that I have friends with children who are reaching the "where do babies come from?" age, I am readying myself with the right answers. But there is an equally tricky question that needs addressing even earlier, as I discovered last weekend when my five-year-old god-daughter challenged me to explain what alcohol was and why grown-ups are so fond of it.

Now that's a tricky one, because it obliges you to be truthful and at the same time to instil some respect for the demon drink. Alcohol, you would like the child to understand, is one of those things, like open fires and pill bottles, that you should approach with extreme caution. It can be nice - it is nice - but it can be dangerous, too. It occurred to me that, had I been French, I could simply have explained that "alcohol is the enemy of poise". Had I been a New York It girl, I might have observed that "alcohol, honey, is like carbs . . . when you're a grown-up you can toy with it, but never actually swallow". Unfortunately, such advice would have been pointless for the British girl, for whom drink, like it or not, is destined to be a significant part of life.

"Alcohol is what grown-ups like to have when they're relaxing," I began confidently. "Because it makes you go bleeeeh," interrupted my god-daughter's seven-year-old brother, flopping around, eyes rolling. "That's only when you've had far too much," I explained, patiently. But what's the point of dissembling when children are used to seeing adults transformed from careworn husks into giggling, Dido-wailing people most Friday nights? And how to explain that, although an adult perk is getting silly, it's not one that they should aspire to?

The problem only increases as they get older and you are expected to lead by example. My 18-year-old niece considers it as my role to take her to bars and nightspots. If I reach for a Caipirinha, she reaches for a Caipirinha or (look away now if you are squeamish) a Southern Comfort and Appletize. It's just about legal, but I am horribly conscious of the pale pink of her liver as compared with the pitted conker-brown of mine. Should I drink virtually nothing with her, in order to demonstrate that the recommended number of units is indeed sufficient? Or should I just knock it back, regardless, and hope that she will observe for herself the loss of motor skills and think: "Eeeewww, not cool." If she wants a Martini, do I give her the Martini lecture (never have two, unless you are already in bed)? Or should I just be relieved that she's not reaching for the Red Bull and Ketamine chaser? Last night, I tried giving my niece the women-and-alcohol talk. "The thing is," she said, "me and my friends have accepted that the years before your twenties are when your body takes a hammering. I'm young and that's just the way it goes." Little does she know.