They are at that tender age when the hormones have begun to stir, and they could be stomping around the room like furious teenagers one minute but snuggling up for a cuddle the next.

The girls are fast approaching 13, the age that Chevonea Kendall-Bryan was when she leaned out of one of the windows on the fourth floor of a block of flats on this street. A boy she knew was down here on the ground, but this was not Romeo and Juliet. Far from it.

Chevonea had been pressurised into performing a sex act on him, and he had shared a phone clip of her doing so with all his mates. She threatened to jump from the window if he did not delete it. Then she slipped and fell 60 feet to the ground, dying from massive brain injuries.

Her mother says she will now campaign against what is happening to young girls in our society. They are certainly under extreme pressure, having to cope with a world more
brutal, more demanding and far more overtly sexual than anything their parents knew.

Never before has girlhood been under such a sustained assault – from ads, alcohol marketing, girls’ magazines, sexually explicit TV programmes and the hard pornography that is regularly accessed in so many teenager’s bedrooms,” says the psychologist Steve Biddulph, currently touring the country to promote a book called Raising Girls.
It is a follow-up to his best-seller Raising Boys – and they are under pressure too, being led to believe that girls will look and behave like porn stars. Our children are becoming victims of pornification.

“It is usually girls who are on the receiving end of some pretty degrading stuff,” says Claire Perry MP, who has just been appointed David Cameron’s special adviser on the commercialisation and sexualisation of childhood. “We’ve got young girls being asked to write their names on their boobs and send pictures. Parents would be really shocked to know this is happening in pretty much every school in the country. Our children are growing up in a very sexualised world.”

So this is the storm my girls will soon face. I can already hear the rumblings. For their sake, I want to know, how bad is it? How widespread? I ask to speak to Mrs Perry, and while I’m waiting for the call back I read a report by the National Society for the Prevention of Cruelty to Children, which suggests it is very bad indeed. Researchers who carried out an in-depth study of the lives of pupils at two London schools in 2010 say that year eight was when they began to feel confused and overwhelmed by sexual expectations and demands.

Claire, who must be 12 or 13, is quoted as saying of the boys in her class: “If they want oral sex, they will ask every single day until you say yes.”
Kamal, a boy in the same year, says: “Say I got a girlfriend, I would ask her to write my name on her breast and then send it to me and then I would upload it on to Facebook or Bebo or something like that.” The profile picture on his phone, seen by everyone to whom he sends messages, is an image of his girlfriend’s cleavage. Some of the boys at his school have explicit images of up to 30 different girls on their phone. They swap them like we used to swap football cards. If they fancy a girl, they send her a picture of their genitals. As one teenage girl said after the report came out, sending pictures of your body parts is “the new flirting”.

Boys have always tried their luck, but now they have the technological means to apply pressure, on phones with cameras and messenger networks that no adult ever sees.
Chloe Combi, a former teacher who began her career in “a pretty posh school”, has written in the Times Educational Supplement about when it goes further: “The hardest conversation I’ve ever had was with a distraught, confused man of about 45. I had to explain to him that we had to exclude from school his seemingly non-abused, non-disturbed, well-loved daughter because she had been caught administering fellatio to a line of young men in the boys’ toilets for cash.”

Ms Combi went on: “A friend of mine, who teaches at another school (much more posh than mine) said that it had got so bad they had to go on patrol every lunchtime to prevent similar incidents.”

What is the cause of all this? We need more research, the experts say. But to a dismayed parent, it seems like the horrific result of a massive experiment. Thanks to the internet, our boys and girls are the first children to grow up with free, round-the-clock access to hardcore pornography. Porn has become part of the adult mainstream, colouring everything from advertising to best-selling books like Fifty Shades of Grey. Of course our children are affected.

Diane Abbott, the shadow public health minister, said last week: “I want to highlight what I believe is the rise of a secret garden, striptease culture in British schools and society, which has been put beyond the control of British families by fast-developing technology, and an increasingly pornified British culture.”

It starts young, with pencil cases that carry the Playboy bunny logo and Bratz dolls that look like they have just finished a shift at a strip joint. High-heeled shoes are sold to girls at the age of eight, along with knickers bearing slogans that on an adult would be meant to sound saucy. Campaigns by concerned groups like Mumsnet only stop products like these for a while, until new ones are pushed out.

The pop industry, which aims at hooking kids before they hit puberty, teaches little girls to bump and grind. I’m not a prude, but I have been called one for asking why a 10-year-old was copying the moves in a video in which Rihanna prowls like a dominatrix and sings, “Come on rude boy, boy, can you get it up? Come on rude boy, boy, is you big enough?”

Working backwards, Rihanna is inverting the more extreme imagery used by some male hip hop stars, whose videos effectively show women as sex slaves. They, in turn,
offer a polished version of the behaviour in hardcore porn, which is only a click away, on imitations of YouTube.

It’s not hidden behind a paywall, it’s free. And you don’t even have to claim to be 18 to watch it. This is not the cheesy porn on the newsagent’s top shelf, which was all we could get our hands on when I was a boy. The extreme, violent stuff our children can see so easily now would make a Seventies porn star blush. Or throw up.
The ubiquity of such material has shifted the understanding of what is normal. Three-quarters of teachers surveyed for the TES last year said they believed access to porn was having a “damaging effect” on pupils. One said girls were dressing like “inflatable plastic dolls” while another said some pupils “couldn’t get to sleep without watching porn”.

However, there is also disturbing evidence that hardcore pornography has become so commonplace that some children see it as “mundane”. The pioneering NSPCC study in 2010 found that watching professional porn was seen by boys as a sign of desperation. They would rather watch – and circulate – home-made porn shots on phones with girls they knew.

This is part of the phenomenon called sexting, the exchange of sexual messages or images by text, smartphones and social networking sites. Chevonea Kendall-Bryan was a victim of it, and worse. She had been bullied by boys since the age of 11, a coroner heard earlier this month. At 13, she was forced to perform a sex act on an 18-year-old after a party. A boy of 15 later demanded the same treatment – or he would smash the windows of her south London home. When she obeyed, he filmed her on his phone and shared the clip around her school.

Sexual pressure can cause girls to contemplate suicide, self-harm, develop eating disorders, or try to lose themselves in drugs or alcohol. But does sexting only happen in the most troubled inner-city schools? No, says Prof Andy Phippen of Plymouth University, who led his own research in Cornwall, Somerset and Devon. “I’ve been into all kinds of schools – including inner city, rural and semi-rural – and I can’t remember a single one where sexting was not an issue,” he says. “It’s not a class thing either. I visit elite schools, and the kids there talk about it just as much.”

However, it is important to say that children may be telling the truth if they insist they have never come across it. Estimates of those affected range from 15 to 40 per cent of pupils, depending on where you are. And when I speak to Claire Perry, she admits: “The answer is we don’t know. I think it is a growing problem. My sense is that even in the nicest, leafiest part of the country, this is something that children are doing.”

Hadn’t we better find out? “Yes. That is why it is good that the debate is happening. Bullying has always taken place, but technology means we have given our children a space where there are no adult eyeballs watching. We have to do something about that. I expect there will be lots of difficult conversations this weekend.”

Over the past few days, she has been accused of being a snooper, after suggesting that parents should read their children’s texts and emails. “If your child was going out with somebody you thought was taking drugs, you would feel you had the right to intervene. Somehow, we don’t feel we have the right to do that in the online world. We are on the back foot. But I think that this week’s reaction shows that parents do want to be able to do this.”

Her first job, though, is to focus on the internet. Last year, Mr Cameron backed an “opt-in” system to block adult content on home computers. The idea has now been dropped, however. A consultation showed that the majority of people thought it too draconian, admits Mrs Perry – but she is now working with internet service providers on a series of changes, including a block on adult content on public Wi-Fi. In the home, customers will have to verify that they are over 18 and want access to adult content, or else restrictions will apply. “You will have to say, ‘I don’t want that filter.’ Once we have this, we will lead the world in online child safety.”

All of which is fine, except it won’t do a thing about sexting. In any case, technologically savvy boys like my 15-year-old will find a way round it if they want to. Of course, he will seek out pictures of people having sex. Boys do. I’m just scared of the effects of the tsunami of hardcore he must see any time he tries. As Claire Perry says: “Porn is a terrible sexual educator and that is not where our children should be getting their information.”

As for his sisters, I shudder. I don’t want them to live in a world in which romance means boy meets girl, boy sends a picture of his genitals. Lily and Rose are not their real names, by the way. I’m that afraid of their being drawn in. We clearly need to talk, awkward as it may be.