There has always been strong disagreement about the true nature of childhood. In the Old Testament, the uncivil children who mocked the prophet Elisha for his bald head were cursed by him so roundly that they were immediately eaten by two she-bears.

No second chance there, but a marked contrast with Christ’s later plea for sympathy with the very young. In the novels of Dickens, the uncontaminated innocence of Oliver Twist is balanced by the cheerful devilry of the Artful Dodger. In the cinema, horror films featuring homicidally evil children coexist with sentimental stories where lovable kids get into only the mildest type of mischief. On the television screens recently, pupils of St George’s Roman Catholic school were seen moved to tears by the death of a good headteacher. Other children of the same age are to go on trial for their part in his murder.

Despite these contradictory images, there is more of a consensus among psychologists about the nature of childhood than existed when the same debate was conducted by theologians or philosophers. The psychoanalytic work of Freud and Melanie Klein suggested the existence of murderous jealousy and sadistic violence in the fantasy lives of small children. Yet apart from the odd psychopath, children generally manage to coexist with their siblings without these fantasies spilling over into dangerous reality. Considering the quantities of unsupervised time that small children spend together, the amount of serious injury inflicted upon one another is small. Inhibition about expressing major aggression in real life seems as natural as the existence of the aggressive fantasies themselves.

But such inhibition, also found in the offspring of other higher mammals when growing up together, cannot be taken for granted if families cease to function. When children are brutalised by bad parents the abuse inflicted upon them may soon be passed down the family chain to those smaller than themselves. Children are also extra vulnerable when society is breaking down. The child soldiers of recent African civil wars have sometimes behaved with horrific cruelty. It is natural for them to imitate the adult example they are set, whether that example is itself good or wicked.

Nor can children even from the most supportive of homes always be trusted when operating in a gang. We are a naturally gregarious species, and collective bad behaviour is often contagious for children anxious to be accepted as part of the group. In William Golding’s novel Lord of the Flies there is only one really nasty child character when the story starts. But most of the rest slowly get sucked into the violence that follows, too afraid to make a stand on their own. The same happens in the bullying of unpopular pupils - or teachers - at school. It is always safest to join in than risk getting picked on. This does not make the bulk of children wicked, but it does make them dangerously vulnerable to bad example put over in a strongly persuasive way.

This means that the adult world can never afford to be passive in the face of serious child aggression. Because child victims so rarely speak out, bullying has gone on unchecked for too long; it is only now that most schools are starting to do something about it. Tough, anti-social gangs of children forming outside school hours must also be confronted. If this means paying youth workers to keep in touch with what is going on in gangland life, as happens in some other European countries, this is an investment worth paying for. The youth service, wrecked by the last 15 years of government economies, has to be resurrected for the sake of every citizen. Pioneering charities like Education Extra, devoted to keeping schools open after hours for supervised activities, deserve every support.

Particular child villains, meanwhile, must be met by greater firmness. This does not mean a return to corporal punishment: there is no evidence that this makes any difference to confirmed young tearaways. But the present situation where children under 14 and in serious trouble can expect to negotiate with social workers rather than with police by way of punishment is no longer working. Most juvenile delinquents still grow out of their bad behaviour when adult; stigmatising such people by imposing custodial punishments when young could eventually do more harm than good. But persistently offending children of whatever age must never feel that they can necessarily get away with what they are doing by virtue of their tender years alone. The option of segregating them from society, however rarely used, could in the long run benefit them as well as the rest of us.

Such policies cost money. But the needs of modern children never come cheap, particularly at a time when play space is limited, parents are often out at work, and violence is portrayed in the media as glamorous and exciting. Schools that concentrate solely upon academic success must be encouraged to spend more time on pupils who may already feel surplus to requirements in a world that only values good examination results. Other long-term remedies will take time, but there is no easy short cut for making peace with today’s sometimes dangerously disaffected young people. Banning knife-carrying (and retailing) may help here, but finding something positive for all young people to do would be far more effective.

Today’s children are all our future. Turning our back on them is not merely to risk a mugging. Those that are disturbed and dangerous now may be even worse if they are still unemployed and unvalued in 20 years time, possibly by then with their own children too. Society has to find a role for all its citizens not just when they are children but when they are adult as well.

If not, those children who feel the future holds out little for them may be even less inclined to behave well in the present.

Nicholas Tucker is a lecturer in psychology and children’s literature at the University of Sussex.