'We tried taking the phone away but he would just get the i Pad from his younger sister. He managed to change the parental controls on our wifi so that only he knew the code.'Children can find sexual material fairly easily on the internet, whether as a result of curiosity or just by accident,' says Carolyn Bunting of Internet Matters, an organisation that educates parents about the risks their children might encounter online.

It gives children a distorted view of relationships In desperation, Sally went to the school and spoke to the headmaster, who called in Matthew and his friends.

It emerged that the 'porn ring' had begun when one of the boys had accessed online porn via video-sharing website You Tube.

Sally says: 'Matthew didn't speak to me for several days after I'd been to the school, but as far as we know the 'porn ring' ended there.

It gives children a distorted view of relationships.

Laura Kay is another mother who was horrified to discover that, at the age of just ten, her son Nathan had been accessing porn.

And this was despite the fact she'd put filters on all the devices in their home.'I'm pretty tech-savvy and thought I'd done everything I could to stop Nathan accessing porn.

So when I found him asleep upstairs, with his i Pad open, and saw that he'd been looking at really hardcore stuff, I was devastated,' says Laura, 43, a social media manager who lives with Nathan, now 13, in Exeter.'Where do they get this terminology from?

I've met these girls in person and they are the most polite youngsters you'd wish to meet.

You'd never dream that they could use words and phrases like that, but they're all doing it.''The Government really needs to take serious steps to stop this.

We, as parents, have to start talking about it, and schools too.' The extent to which porn is affecting our children in the long term is something experts can't agree on, but psychologist Professor Geoffrey Beattie says young people may be more damaged than we realise.

He is most concerned about the potential for psychological harm caused by 'flashbulb memories'.