he seven-year-old daughter of a colleague of mine recently asked him a difficult question. She had been reading a magazine targeted at her age group - the pound;31 million battleground of publishers and advertisers to win the pocket money of Britain’s youngest consumers. At the end of an interview with Britney Spears, she turned to her dad and said: “What’s a virgin?”.

It is a reminder of the way the language and images of adult life now seep remorselessly into the consciousness of society’s youngest members, and the way the traditional boundaries of childhood are withering away.

Once there were children. Now, in the eyes of many advertisers, there are tweenagers.

An academic recently called for Shakespeare teaching to be made more relevant by linking it to Big Brother. Shakespeare’s characters, he suggested, would mean more to youngsters if they were presented as contestants in the Channel 4 show.

If your child is a regular visitor to the CBBC or Newsround website, or a reader of Sneak or CosmoGirl!, then they will have read features that locked into the early summer mania that accompanied Big Brother. All of which, you might say, is harmless fun. Yet this is the TV show that led to a frenzied front-page debate about whether two of the contestants had had oral sex.

It is part of the “pornification” of Britain in which the language and imagery of pornography is used to sell everything, where even an advertisement for Pot Noodle has to be banned for its sexual suggestiveness.

If you took your child to buy a new school uniform this summer, then you probably walked past a French Connection store with their unsubtle punning t-shirt logos: “Where the fcuk are you?”, “Too busy to fcuk”.

It is as if we have given up on the traditional demarcation of adult life and childhood. So while we have extended adolescence to 40 and beyond, it looks as if we have shrunk childhood to eight and below.

Media executives will sneer that this is a typical middle-class, middle-aged, middle-England response. But they misunderstand my point. It is not an attack on pornography in itself. Instead, it is a concern about the way we seem to be giving up our traditional responsibilities to protect children.

Childhood, and in particular adolescence, have long been an initiation for young people into the responsibilities of adult life. Most of us spent our teenage years wishing we were older, but tantalisingly had to wait.

A survey this year by BRMB showed that 94 per cent of 12 to 17-year-olds have mobile phones. Sixty-seven per cent have computers and regularly surf the internet. Both of these figures are far higher than in America.

Net monitoring agency NetValue found that one in five online under-17s used porn sites - for an average of 28 minutes.

Many adults now believe children are fair game in a marketers’ world. As the editor of CosmoGirl! said in the Guardian: “In London, 12-year-olds are as sophisticated as many 16-year-olds.”

And that is my point.

In a technological society that demands more self-discipline and personal responsibility from all of us, society appears to have given up emphasising such things. Just when children need us most to cope with a society of dizzying confusions, we have abandoned them to values that emphasise self-gratification and materialism.

In schools we continue to promote values we assumed most of society also stood for - how to speak politely, how to behave appropriately, how to take an active part in the community.

But these things cannot be left to schools alone. Society dismantles childhood at its peril, leaving teachers marginalised in assuming a moral responsibility which so many other adults appear to have abdicated.

Geoff Barton is headteacher of King Edward VI school, Bury St Edmunds