Bad boy: Tilda Swinton and Rock Duer in We Need To Talk About Kevin
Like many parents who've witnessed their children being spiteful or cruel, I felt an icy chill in the stomach. Most parents want their children to be kind and considerate most, if not all, of the time.
But while nearly all youngsters have aggressive moments, for the vast majority - including mine - those moments pass and five minutes later they're demonstrating their sweet, kind natures by giving you a spontaneous hug or sneaking the cat a kitty treat.
For a few unlucky parents, that frightening chill never leaves them. Instead, it grows into a gnawing, aching certainty that something is dreadfully wrong.
The problem might show itself in a child's persistent inability to feel empathy when others are hurt or in pain. It might be the child's complete lack of remorse for misbehaviour. In the most worrying cases, the child is cruel to other children or animals.
One day these parents will ask themselves a terrifying question: Could my child be a psychopath? And, say experts, the answer could well be yes. For psychologists now believe it is possible to identify psychopathic traits in children as young as three.
It's a controversial area, particularly as certain characteristics of adult psychopaths - narcissism and impulsiveness among them - are rife in every nursery.
But experts - backed by practical and scientific evidence - believe that identifying children at genuine risk, and intervening early, could make a huge difference to the course of their lives and their consequent impact on society.
Stephen Scott is professor of child health and behaviour at the Institute of Psychiatry, based at the Maudsley Hospital in South London. As director of the National Conduct Problems Clinic for children aged between three and eight who show disruptive, difficult and anti-social behaviour, he is able to identify those who exhibit the 'combination of anti-social behaviours with an overlay of callous, unemotional traits' that are typical of adult psychopathy, and refer them on to the department's Tender Loving Care (TLC) Project.
This research programme sees 100 children every year who have been referred by consultant psychiatrists, consultant paediatricians, social services, GPs, educational psychologists and teachers. Parents can also take along their own child if they are concerned, without a doctor's referral.
Professor Scott says: 'Adult sociopaths are superficial and charming, but can also seem uncaring and heartless.' He believes these characteristics can be identified in childhood.
Diagnosis of a child with 'callous, unemotional traits' (often shortened to CU) is complex, he explains, but usually they get into serious trouble leading to being excluded from school before they are put forward to be formally assessed.
Most of the children referred to him are diagnosed by a combination of special tests and in-depth interviewing about their behaviours and emotions. Psychologists also speak to the child's mother, and get information from the school.
As well as callous, unemotional traits, they may show a persistent lack of guilt about wrongdoing and a lack of empathy across all situations and relationships. Professor Scott adds: 'Normal people can understand other people's feelings and also care about them. So if you take a bunch of kids, and ask them what happened to little Johnny who fell over, cut his knee and cried, typically-developing children will understand what happened and empathise.
'Autistic children really can't understand what it's like to be someone else, whereas callous, unemotional children can understand, but they just don't care.
'So if a parent is concerned about their child, they might ask themselves: "Is it that my child understands and doesn't care, or is it that they just don't understand?" It's an important distinction to make.'
While Professor Scott is wary of 'over-diagnosis' and emphasises that many children and adults can possess the cold, unfeeling nature of the psychopath without actually being one ('think boyfriends who couldn't give a damn and some chiefs of big corporations') there is little danger of confusing the average five-year-old scamp with the fledgling psychopath.
'I have children in my clinic who have no remorse, steal from their parents, enjoy taunting them in a way that shows they couldn't care less, despite being well-loved,' he says. 'This behaviour, if sustained and widespread, is likely to lead to a diagnosis of psychopathy.
'One five-year-old girl held the much-loved family cat out of a top-floor window, then hurled it upside-down onto concrete, just for pleasure. Cruelty to animals is a bad sign. That is more characteristic of a child with callous, unemotional traits than fights with siblings.'
Indeed, allaying the fears of 99 per cent of the nation's parents, Professor Paul Frick, who has studied child psychopathy for two decades, says: 'Most of the time, we don't pay any attention to what siblings do to each other. The children we are concerned with are not just misbehaving in the home. 'They are constantly hurting people in a cold and calculated manner, in many different situations.'
While these children show deep, extreme anger, it is different from the explosive, reactive rage of other children with 'hot-blooded' conduct disorders. One little boy who researchers saw on the TLC Project had pushed his mother down the stairs and told her that he 'liked hurting people'.
'We don't like to label children as pscyhopaths,' says Professor Scott. 'But we would say this child has traits which, if they persist are likely to lead to psychopathic tendencies.'
The parents of another 12-year old had just spent £300 on a picture window. Professor Scott says: 'The boy, looking at his parents, went up and smashed it. It wasn't out of rage: it was intentional.'
These children are, admits Professor Scott, hard to treat. He cites biological differences: 'There is a part of the brain called the amygdala, where you process fear.
'They don't seem to process fear that much. This makes them more able to be risk-takers.' One expert cites a six-year old who would sneak out of his room at night and wander the neighbourhood. 'They like rewards, but don't care about punishments.'
Yet there is much that parents can do to help. The TLC Project involves two weekly sessions with the children and six with parents (free of charge).
Professor Scott says: 'These children tend not to look at their parents' eyes, and the notion is that if you get them to look, they recognise emotions better.
'So we get parents to look them in the eye, to say, "Look at me: I'm very pleased when you do that," to get these children to understand the emotional components of interaction, to activate this centre in the brain that seems underactive.'
While adult psychopathy is difficult to treat, experts believe that if those at risk are spotted earlier, the unhappy trajectory of anti-social behaviour and its consequences may be averted.
Professor Scott advises parents: 'Give these children clear consequences. They're smart so you have to be strict about following through with threats such as: "If you do that, you're being sent to your room." And it all needs to be said very calmly.
'This advice also applies to other kids, but you've got to be even firmer with these children.'
No one is claiming it's easy: parents of CU children could be forgiven for shutting down emotionally themselves, but Professor Scott says: 'That doesn't work. They need lots of positive talk, such as: "Well done for not losing your temper," and quick rewards like: "Because of that you can choose pudding tonight." Fast responses and calm, consistent parenting.
'It's also important for parents to gain their children's respect and have lots of positive interaction together. Ten minutes of special time a day makes a huge difference.
'The other thing is when they're being naughty, don't get into lengthy discussions. Just say: "You've done this, there's the consequence," and turn away. As soon as they stop showing any anger, turn back, and talk normally again. Give them attention for normal behaviour. It's hard to do - we practise that with parents a lot.'
Research is also forging ahead in the U.S. One mother whose nine-year-old attended a course of treatment for CU youngsters run by Dan Waschbusch, professor of clinical child psychology at Florida International University, admitted she was unsure if her son had improved - or merely learned to manipulate others with more sophistication.
But Professor Waschbusch argues that, essentially, it doesn't matter: 'My belief is that we can improve their outcome. They will be productive, happy citizens.
'Whether we can shift them so they experience empathy the way other people do, I'm more sceptical. But that may not be needed.'
10 Tell-tale Signs
1. They persistently hurt, bully or fight others, or violate their rights by stealing or vandalising.
2. They break major rules, such as running away from home or staying out late.
3. They show no guilt when told off for doing wrong, e.g., pushing another child into the road.
4. They show a persistent callous disregard for other people's feelings - not just siblings (e.g., pushing another child off a swing and being unmoved by their distress).
5. They persistently don't care about how well they do in, say, school, even when the expectations are clear and they are capable.
6. They seem cold and unfeeling, only showing emotions to intimidate or manipulate.
7. They blame others for their mistakes, rather than accept responsibility themselves.
8. They are fearless and like doing novel and dangerous activities.
9. They are unmoved by the threat of punishment (e.g., 'if you do that, I am going to take away your bike').
10. They are highly motivated by reward or what they'll get out of something, even if it hurts others (e.g., stealing).
"The parents of another 12-year old had just spent £300 on a picture window. Professor Scott says: 'The boy, looking at his parents, went up and smashed it. It wasn't out of rage: it was intentional.' "