Give Me a Break:Tonight, my teenage daughters and I are going to find out whether Stephen Fry has HIV when he shares his test results with viewers. We were riveted last week to the first part of his two-part BBC documentary, even though it was challenging and ugly at times - especially when it described gay men deliberately trying to catch the virus.

But it was also inspiring, especially when Fry introduced us to the 19-year-old who was born with the virus because her mother had it and didn't know it. This girl had faced up to the bullies who daubed insulting slogans on her house and decided to become a spokeswoman for teenagers living with HIV.

And now we know how most people get HIV. They have casual sex with a lot of partners and don't use condoms.

This is reality-parenting, 2007.

I don't know how parents managed to educate their children about sex before TV came along. Older people from rural areas say their main information came from observing farmyard animals. In the 21st century, that's why we have the Discovery Channel. Elephants having sex, exotic insects having sex, horses giving birth to hybrid zebras - whatever. Watching these programmes as a family is an opportunity to discuss procreation without embarrassment.

Because deliberately bringing up the subject is a major no-no, especially once children reach the age of reason (age four?). Even those well-meaning children's books that are meant to help us "talk" about "it" can backfire. In our house, the well-meaning illustrated book for under-eights and their liberal parents, Where Willy Went, still provokes hilarity at the mere mention of the title.

Kids get a certain amount of sex education in school (laughable, mostly, from what I've heard, with anything memorable coming informally via the playground), but it's my responsibility to ensure that my children grasp the wider context. I want them to have the information they need to think for themselves and make life-enhancing decisions rather than mistakes, even if mistakes are life-enhancing in their own way, as I constantly remind them, having made so many myself.

Kids need to know about the real world, which is why I don't approve of parents who try to protect their children's "innocence" by banning TV (apart from censored DVDs), interactive computer games and the internet. Banning screen-time is like living on a boat and refusing your child swimming lessons. The information society is the one our children will live and die by.

I imagine these parents are the types who still believe they can deliver sex information in one all-encompassing "birds and bees" chat of the sort you see on the Christian channel, though I'm probably wrong. But I do know I'm right in believing that reality is rather more Fellini than Disney. Children see things, hear things, talk to other children.

Their process of enlightenment about the thing we call sex (as if three little letters were enough) is an incremental trickle of thousands of shy questions, which arrive usually when you least expect them. Like in the middle of lunch with the in-laws. When they're tiny, they're usually satisfied with the explanation that "when a Mommy and Daddy love each other (after they've both got university degrees, got married and bought a house, I've always hastened to add) their love grows inside Mommy to become a child". But that window of opportunity lasts about a New York minute. Pretty soon, children realise that your explanation was a bit sketchy, depending on how precocious they are in that Montessori you've spent a fortune on.

I've heard parents say that children should be allowed their "innocence" for as long as possible, but I wonder if these parents really mean that they're more comfortable with their children being "naive". There's a fine line between innocence and naivety. Innocence means inexperience, virtue and purity. Naivety means gullibility.

To me, innocence has a lot of strength in it, because it's about believing in the integrity of your own body and not allowing anyone to talk to you or touch you in a way that makes you feel uncomfortable. You can know all about HIV and unsafe sex and still remain innocent in the sense that you have chosen to remain inexperienced for the time being. For teenagers to remain truly innocent for as long as they desire to be, they need to be armed with enough information not to be naively gullible with the first person who says "I love you and if you love me we'll do it and we won't use a condom".

Which brings us back to Stephen Fry. So far he's shown us that protecting yourself against HIV isn't just about sex. It's about having relationships of integrity. It's about loving yourself so much that you realise no one is worthy of your love if they expect you to risk your health. The sort of sex you have without a condom is about ignorance, or if not, lust and self-destructiveness, rather than love.

Tonight, Stephen Fry's revelation will help us have yet another one of the many small exchanges that gently bring us along to the bigger picture about sex.