You don't want your son to be bullied. You don't want your daughter to be groomed by a paedophile. You don't want your teenager to be defined for the rest of his or her life by a moment of madness that's best forgotten. So you 'friend' your child on Facebook.
I can see the logic. I really can. As parents, we're bombarded by warnings about internet use. Most of us, unlike Stephen Fry, are not at the cutting edge of technology. We've heard about Kindle and iPod apps, but we're not sure we completely understand the pitfalls of social networking. So we'd rather play safe. We'd like to keep an eye on what our offspring get up to, just as we did years ago, watching them build Lego towers while we did the washing-up at the sink.
But isn't being your child's friend on Facebook going a bit too far?
The stakes are high - I realise that. Employers check out Facebook profiles. So do people handling university admissions. So if your teenage son has a picture of himself in a yellow morph suit larking about with a can of lager and a shaved head, it might well come back to haunt him when he's applying for a senior management position at Unilever. (Maybe it wasn't a good idea either for Gary Lineker's party-loving son George to suggest on Facebook that not getting the grades he needed to study at Manchester University was somehow his school's fault...)
The internet is not just the fast-moving present. It's also an underground vault full of skeletons. The busy people called 'reputation managers' know all about this. They make a living trawling internet files for all the stuff you wish you'd kept private in the first place.
I understand that cyberbullying is a real worry. A mean comment - and a Facebook wall is such a public place - can feel like the end of the world. My 16-year-old daughter says you shouldn't put anything up on Facebook that you wouldn't be happy to say to someone's face.
And I completely understand the ever-present anxiety about predatory perverts. There's a strong argument that parents should reinforce the message about privacy settings (and untagging photos if you'd rather not have them linked to a profile). It's not always wise to give out too much information - and maybe you have to be old and cynical to understand that.
But can't all this be handled in a conversation? Isn't it better to talk about the dangers of paedophiles, bullying and online reputations up-front?
I don't like the idea that we have to hover round the edges of our children's social lives just to check that our greatest fears haven't become reality. This is partly selfish, I know. I'm not on Facebook, and I don't want to be. I feel like someone hanging on to a horse and cart when everyone else is driving a car, but I'd much rather socialise face-to-face than on a screen.
But it's also because I feel that becoming your child's friend on Facebook is sort of missing the point. It's like hiring a private detective to trail your husband. If you really don't trust him to tell the truth, isn't it about time you sat down and talked about what's going wrong?
If you monitor your son or daughter on Facebook, you're going to end up getting things wrong. You'll misunderstand the references. You won't get the jokes. You'll worry about why Sam hasn't answered or whether Jude is being weird. It's like being in a foreign country where you don't speak the language. You'll be the dotty distant relative at Christmas making mad irrelevant remarks, or the desperate friend who tags along to a party even though everyone would much rather you stayed at home. Look at you, Dad-dancing in the corner, Uncle Bryn with his Sat Nav.
Facebook started at Harvard. It spread to other universities, then to secondary schools. Now it's open to everyone. But to me it still feels like it belongs to people under 25. I don't go to teenagers' parties. I don't skulk about in hedges trying to eavesdrop their conversations. I don't read their diaries, hack into their email accounts or monitor their texts. So why would I want to supervise what they're doing on Facebook?
There's a really difficult line to tread between protecting your under-18s and finally letting them go.
Being a friend on Facebook is, I think, a step too far.
What do you think?
Are you your child's Facebook friend?
If so, do you find yourself checking on them?