A health watchdog has issued guidelines to help parents distinguish between naughtiness and more worrying behaviour in their children that might need medical intervention.About one in every 20 children aged five to 16 has a conduct disorder - persistent and extreme misbehaviour.The National Institute for Health and Clinical Excellence guidelines outline how to spot and treat these conditions.They say parents should play a central role in this.While all children can be naughty from time to time, the behaviour of children with conduct disorders is different.They persistently misbehave - both at home and in school - and their actions can be extreme and harmful.As well as stealing, fighting or vandalising property, they might hurt people and animals, for example.Prof Steven Pilling, who helped develop the guidelines, said: "Children with conduct disorders are different. It's not a bit of tantruming or getting into trouble now and then. It's picking up the 14in TV and throwing it through the window."He said it was important that parents be taught how to handle this type of behaviour.Pointless punishment"Firmness and saying 'No' is not the solution for these children. We need to get parents to switch the focus from being controlling and punitive to encouraging positive behaviour," he said.About half of children with antisocial behaviour or conduct disorders not only miss out on parts of their childhood but also go on to have serious mental health problems as adults. Some go on to be repeated offenders.The National Institute for Health and Clinical Excellence (NICE) and the Social Care Institute for Excellence (SCIE), who jointly developed the guidelines, say early intervention is essential to break this chain.Prof Peter Fonagy, a professor of psychoanalysis at University College London who co-authored the guidelines, said: "All children can be naughty, defiant and impulsive from time to time, which is perfectly normal. However, some children have extremely difficult and challenging behaviours that are outside the norm for their age."Recognising and accurately diagnosing a conduct disorder is vital to ensuring children and their families are able to access the treatment and support they need to manage the condition."Fiona is a mother of a child with a conduct disorder. She said: "It is not just the child who is affected by a conduct disorder; it can have a significant impact on their brothers or sisters, their parents, family members, teachers and other people they come into contact with."Real practical support and advice is needed to help parents manage their child's condition, such as what to say to calm the child when they are very distressed to avoid inflaming the situation."