A unique insight into why young children sexually abuse other children is to be revealed in a ground-breaking study.

The research, which has yet to be formally published, was on boys aged 10 or under who have molested siblings, classmates, or friends.

It found that they are invariably born into families in which abuse, violence and neglect has become routine over several generations.

The peer-reviewed study found that the boys were unable to form healthy relationships as a result of neglectful and hostile parenting.

Even before starting school, they were anxious, angry and detached; bed-wetting, nightmares, self-harm and eating problems were common.

All of the boys in the study, which is to be published in Child Abuse Review next year, started abusing after being sexually abused themselves.

By the time they received specialist help they had all perpetrated serious abuse against several children. Their victims were as young as 6 months and penetration and violence were common.

The research, conducted in the London-based National Clinical Assessment and Treatment Service, found that the authorities, as well as teachers, social workers and doctors, often missed numerous opportunities to intervene.

Colin Hawkes, the study's author and NCats service manager, said that professionals often ignore, dismiss or punish early warning signs such as a child exposing himself or talking explicitly about sex because they find it difficult to believe that children are physically or emotionally capable of such things.

The study also found that in a third of the 27 cases in its sample group the birth mother was suspected of sexually abusing her child. But this social taboo was never tackled by the authorities.

The study asserts that in many cases the abusers copy what adults around them are doing. They may also be seeking control in response to the cruelty and loneliness of their own lives, while spoiling the life of a "luckier or happier" child. Researchers were most shocked to find that many of the boys had learnt to groom and target vulnerable children.

The findings add to growing evidence about the devastating impact of early childhood abuse and neglect on brain development, which can lead to serious violence against one's self and others in later life.

Hawkes said: "This small minority cannot think straight. They have never experienced calm, coherent parenting. By the time we see them they have been spinning through a spiral of thoughts and feelings and sexually harmful behaviours for years. Early intervention is key as the longer you leave it, the more likely these harmful patterns become fixed [in the brain]."

- INDEPENDENT