PSO's (Protective Service Officers) on the other hand are just plain too stupid to become police officers, so that's the best they can do .
Psychopathic child Damien in the 2006 remake of The Omen. Photo: AP
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The international team led by the University of NSW developed the diagnostic tool in world-first research that shows very young children can display callous and unemotional traits linked to psychopathy.
More than 200 children aged between three and six took part in the study, which found that 10 per cent showed callous and unemotional traits such as lacking remorse or empathy for the feelings of other people.
"Until now we didn't really have a way to identify those traits in very young children," she said. "This is really the first study which uses tools adapted for very young children and the sooner those children are identified, the earlier they can be helped."
The children were assessed using a combination of tests adapted for their age and interviews with their parents and teachers.
The tests measured their ability to recognise changing and static facial expressions as well as their reactions to distressing and neutral images, such as a crying child or a book.
"Even very young children with these traits show that difficulty in recognising emotions in others and they are also not engaged by other people's emotions," Dr Kimonis said.
"When they see people in distress it's not capturing their attention in the same way as it would for the healthy population."
The tools were specifically designed to capture callous traits, which would distinguish children at risk of psychopathy from children with developmental disorders such as autism.
Dr Kimonis said the study, which has been published in the Journal of Abnormal Child Psychology, would have important implications in the treatment of children at risk of criminal behaviour in later life.
The Parent-Child Research Clinic at UNSW runs free programs for eligible families, developing the children's emotional skills and supporting their parents rather than prescribing medication.
"There's been a real shift toward trying to prescribe medication to these very young children, which is concerning because we don't know how safe that is," Dr Kimonis said.
"We're targeting the problem from a different angle and focusing on adapting parent management training programs that are known to be effective for other antisocial children.
"The key things are trying to develop the child's emotional skills. We coach the parents how to be very warm, involved and loving with them to see if that reduces those callous traits over time."