"He's like a Jekyll and Hyde, an angel one moment and a monster the next," says the distraught mother of a 7-year-old. Most children can be little monsters at times but there are some who seem to be permanently uncontrollable whatever their parents do. Hyperactivity is one of the most controversial conditions in child psychiatry. In older children it can lead to vandalism and serious crime. Is it due to food additives, brain damage or just bad parenting? Tonight's programme reports on new research which has produced surprising answers, bringing hope for at least some of the little monsters.