"Then what on earth should I tell her," I said, "when she asks how babies are born?"
"I tell mine the fairies brought them," she replied primly.
When I'd finished laughing I wondered who had the right approach.
I've always maintained that one shouldn't lie to children, except about harmless things like Father Christmas being real and the fact that the ice-cream van has run out of lollies again.
But that means that my children, aged 4, 3 and 3, know exactly how babies arrive. When my four year old son asked what willies were for, I told him. When his sisters wondered how exactly babies got into Mummy's tummy, I gave them a lesson in glorious technicoloured detail.
To my mind there are only three ways to approach a direct question from a child about sex:
1. Tell them they're not old enough to know
2. Concoct some cock and bull story about the stork and/or fairies
3. Tell them the truth
The first two options are frankly patronising, so that really only leaves the third.
I tell my pre-schoolers exactly how it all works. And you won't find me spouting any nonsense which starts with 'well the daddy has a seed and he plants it in the mummy's tummy' – the very thought of it makes me cringe.
My explanations involve penises, wombs and every bit in between. I stop short of diagrams and anatomically correct dolls, although I'd never say never.
I'm not the only mother insistent on this level of honesty when it comes to the birds and the bees. Mum-of-three Emma tells me she's been straight with her children right from the start. "My daughter was two when she first asked how babies were made, so I explained about sex. I made it clear that it was something which only adults did, and used language she could understand."
Far from provoking a deluge of complicated questions, Emma's approach seemed to do the trick. "Olivia thought for a while, then went back to playing with her toys and hasn't mentioned it since."
Like me, Emma believes it's important to tell the truth to kids, no matter how old they are.
I wouldn't lie to them about anything else, so why about sex? If they're old enough to ask the question, they're old enough to hear the answer.
The idea of sex education at such a young age horrifies Hazel, mum to one year old Olivia. "There's plenty of time for all that when they're older," she says, "so why spoil a child's innocence by telling them too soon?"
Olivia's too young to ask awkward questions right now, but Hazel plans to simply side-step the issue. "I won't tell her anything about the birds and the bees until she learns about it in school – I don't want to confuse her or encourage her to think about sex."
So what's the official line on sex education? Is three really two young to hear how babies are made? The subjects taught in schools as part of a sex and relationships education programme differ across England, Wales, Scotland and Northern Ireland, but all children will receive some compulsory sex education as part of the Science curriculum.
As a basic rule, children aged 5 to 7 will learn how animals and humans reproduce, and how to recognise the male and female external parts of the human body. So if that's what our children will be learning in primary school, then surely it makes sense to prepare them before they go?
To my mind, teaching kids the basics of sex education is no different to practising letters and numbers before they start school, but Hazel disagrees. "Reading and writing are essential skills and something children need from an early age. Sex isn't something they need to know about until they're approaching puberty – it just isn't appropriate."
Every parent knows the right approach for their own child, and each family has different values in relation to sex and relationships.
I believe firmly in honesty and openness when it comes to answering my children's questions, so I'm always ready to explain what a vagina is for, why willies get big and why that woman in the swimming pool has hair there.
I just wish they wouldn't ask me so loudly.
What do you think? Is it best to answer children honestly, or side step the sex talk?