I did a double take yesterday when I was tracking a conversation on Twitter to find the original Tweet (about a TV show) had come from one of my niece’s friends – a 9 year old. Seriously? Why would a 9-year-old need a Twitter account?

Twitter is fun and great and useful, and my Tweets in particular really are quite marvellous.

But Twitter is completely uncensored and home to countless thousands of offensive accounts carrying messages, links and images of pornography, violence, racism, pro-suicide, pro-anorexia, or any combination of the above.

Maybe your child is only following Dr Who, the Moshi Monsters and Disney Channel but it's a moment's work to type a rude word into the search box. It's the 2011 version of what we used to do on the school bus home, when we went looking for the rude pages in Judy Bloom. The difference being that the worst thing about Judy Bloom was never being able to meet someone called Ralph without sniggering. The worst thing about Twitter? Could be a good deal more sinister.

I feel even more strongly about kids on Facebook. It makes me sad when I see parents who I know would be horrified at the thought of their kids walking home unsupervised, allowing their kids to have Facebook accounts.

"Oh, but my daughter’s Facebook account is private, and I’m her friend," you say.

That's lovely, dear.

But I can guarantee it will take your 9-year-old and her friends about two minutes to work out how to add Mum and Dad to a special friendship list that means they don’t see half the updates on the network, and certainly none of the interesting stuff. 

And Facebook isn’t just about who’s on your child’s friendship list. I’ve yet to see a single Facebook account that’s completely locked down – Facebook makes it virtually impossible to achieve.

The odds are if your friend posts a photo on Facebook and you comment on that photo, all your friends can see the photo. If you comment on a friend’s status update, all your friends can view that status update.

And the thing about Facebook is there’s absolutely no guarantee that person with a photo that looks like a 12-year-old kid actually *is* a 12 year old kid. So your child makes friends with someone because they are already friends with their best friend. You have absolutely no way of guaranteeing the identity of that person, who now has access to all kinds of information about you.

You can right-click on any Facebook photo and save it to your own computer. I’ve seen two stories this month about teenage girls who have had photos stolen from Facebook and found them on porn sites. Try explaining that to your future university admissions panel or potential employer.  

You might track the messages on a Facebook account by having them sent to your email address, but that only tracks incoming messages, not outbound. And it doesn't allow you to track Facebook chat. Or the links your child might follow to websites and applications outside Facebook itself.  

I’ve worked as a technology journalist for around 12 years now, and I’ve yet to find a single expert who thinks it’s a good idea for kids to be on social networks.Yes, there are all sorts of guidelines about protecting children on Facebook. But surely the bottom line is that children don’t need to be on Facebook or Twitter.

They don’t need you to lie about their age so they can access something that isn’t designed for them to use. They don’t need a Twitter account and they don’t need a smartphone – unless you’re hoping to teach them street smarts by letting them get mugged a couple of times. 

What do you reckon? When do you think the right age is to use Facebook and Twitter?