The fact that I have just had one doesn't change a thing: children, I tell you, are the devil's work. They lure you in with their gummy smiles, flatter you with squeaks of joy, wrap themselves around the tenderest parts of your psyche and squeeze and squeeze until the critical faculties pop right out of your skull. How else to explain the apparent amazement that greeted the news this week that Britain's children don't always play nicely?

Our little cherubs, it transpires, are more than a little homophobic. A survey by the Association of Teachers and Lecturers found that "gay" is now the most common insult in the classroom, with 70 per cent of teachers having witnessed homophobic bullying among pupils. "Bitch" and "slag" were also popular, and pupils delighted in spreading malicious rumours about each other's sexuality.

To some extent, it was always thus. Children have an almost primeval instinct for bigotry, whatever their background or upbringing. "Gay", "slag" and "Jew" (to denote meanness) were the insults of choice some 30 years ago at my impeccably liberal primary school in Oxford. My classmate's parents – left-leaning dons and novelists, of the type who might have dabbled in Judaism or ideological lesbianism themselves – would have been aghast at the reactionary filth pouring from their offspring's rosebud lips.

Since then, however, there does appear to have been a shift in the tone of playground prejudice. Whereas in my day "gay" most definitely meant homosexual (even if we weren't entirely sure what that meant), today it is used as a general expression of disdain. A pair of trainers can be gay, or a broken toy, or anything that is malfunctioning or undesirable.

There are some who say that this broadening out of meaning makes the insult less troubling: that it is hardly homophobic at all, so much as a quaint reworking of the language. That is wishful thinking. It is the very ubiquity of the insult that makes it so insulting. If everything that is rubbish is gay, then gay people themselves are no better than rubbish. The contempt is all the more brutal for being so casually delivered.

A flippant insult, moreover, is harder to combat. Perhaps the most disturbing revelation in this week's survey was that 50 per cent of teachers said they did not dare challenge pupils who used homophobic abuse in the classroom. They offered a range of excuses for this pusillanimity: the insults were used in a "joking" manner; the problem is so ubiquitous as to be incurable; the teachers were afraid of being seen to promote homosexuality, or of becoming a target themselves.

The alternative to turning a blind eye seems to be surreal overreaction. A friend of mine relates how her five-year-old nephew was sent home from school for calling someone a lesbian. His mother was ordered to stop him using that word. Her protestations that she couldn't possibly, since that would imply there was something wrong with lesbians, met with pursed-lipped incomprehension: she is now marked down as a "difficult" parent.

In truth, it is impossible to outlaw homophobic bullying without becoming embroiled in semantic absurdity. And neither is it really necessary. It is bullying that is the problem, whatever linguistic form it takes. The Darwinian struggles for survival that take place in the average playground can make a brute of even the gentlest child. Teach him empathy, good manners and respect for others, and he will start to see for himself why homophobia, racism and all the other manifestations of that brutality are wrong.

Of all the many schools I went to, only one was entirely free of bullying: a tiny convent in Twickenham, where the nuns had a genius for inventing hundreds of tiny, pettifogging rules. Wearing the wrong kind of shoe in the gymnasium could earn you a month's detention. I once got suspended for chewing bubble gum. It was so easy to be naughty that we could afford to be nice.

Under the benign dictatorship of the nuns, the worst possible crime was rudeness. It would have been unthinkable to hurl abuse, homophobic or otherwise, within earshot of a wimple: and because we couldn't do it in public, we became disinclined to do it in private. Of course, the nuns had the advantage – rare these days – of not wanting to be down with the youth. They had no trouble imposing discipline because they were not afraid of our scorn, and their fearlessness generated respect. They were able to keep our baser primeval instincts in check, long enough for us to learn to do it for ourselves.

That is what growing up is all about: transforming ourselves from cute little barbarians into creatures of civilisation. And it is up to us adults – parents and teachers – to lead the way.