The age of innocence is over

Martin Daubney, who for many years edited a magazine called Loaded, is now a father of a four-year-old boy. He writes at Mail Online about what thirteen-year-olds know about sex.

It seemed as if the children's entire expectation of sex had been defined by what they see in online porn. He has produced a documentary which will air in Britain beginning tomorrow.

A girl added, 'On Facebook, you just scroll down and it's there. If any of your friends like it, it comes up on your home page.'

'I find it dirty and disturbing,' said one 15-year-old boy. 'I try not to look at it, but people just keep sending it to each other. They email disgusting links to each other's mobile phones to shock.' One girl put her head in her hands and said, 'It's just gross'.

It's horrifying enough for parents to know that children can get porn via the internet. But to think they get it from Facebook - the social media currency that has become a universal must-have for teenagers globally - will strike terror into their hearts.

I asked the teenagers: 'On a scale of one to ten, how likely would you say it is that boys and girls your age are watching porn online?'

The reply was a chorus of tens, nines and one eight.

When I asked the children if there were parental controls on the internet at home, they all said no, their parents trusted them. They all admitted their parents had no idea what they were watching, and would be shocked if they did know.

According to the survey, the boys appear largely happy about watching porn - and were twice as likely as girls to do so - but the girls are significantly more confused, angry and frightened by online sexual imagery. The more they see, the stronger they feel.

I feel as if an entire generation's sexuality has been hijacked by grotesque online porn.

Daubney set out to find out what porn is doing to the brains of people eho are addicted to it. He enlisted the help of Dr Valerie Voon, a neuroscientist at Cambridge University and a global authority on addiction. She was interested in a particular brain region called the ventral striatum - the 'reward centre' - where our sense of pleasure is produced. This is one of the areas where an addict will show a heightened response to visual representations of their addiction - whether it's a syringe or a bottle of vodka.

What we discovered was a revelation. When shown porn, the reward centre of normal volunteers barely reacted, but that of the compulsive porn users lit up like a Christmas tree.

If porn does have the insidious power to be addictive, then letting our children consume it freely via the internet is like leaving heroin lying around the house, or handing out vodka at the school gates. And this toxic effect is filtering down directly into young girls' lives.

We learned that the teenage brain is especially vulnerable to addiction.

The brain's reward centre is fully developed by the time we're teenagers, but the part of the brain that regulates our urges - the pre-frontal cortex - isn't fully developed until our mid-20s. The brains of teenagers are not wired to say 'stop', they are wired to want more. The implications of this study are profoundly troubling.

So who is going to take on the responsibility for protecting our children until they are old enough to do it for themselves?

If we stick our head in the sand, we are fooling only ourselves.