Magistrate Karen Fryar issued the warning in sentencing the boy, who cannot be named because of his youth, on charges of committing acts of indecency and sexual intercourse with a person under 10.

The ACT Children’s Court heard the offending occurred over a number of months in 2012 and involved the boy’s three cousins, all aged 10 or under.

The boy, then aged 12, showed the girls pornographic material and cajoled them to touch him. He also touched one of the girls.

The court heard the boy came from a supportive and loving family, was intelligent, and excelled in all aspects of his schooling.

His parents reported he cried constantly and isolated himself after the offences were disclosed.

Ms Fryar handed down her decision last month, and the judgment was published this week.

Magistrate Fryar convicted the boy and ordered him to sign a two-year good-behaviour order, which includes he accept supervision and attend counseling.

Ms Fryar said the actions of the offender went beyond youthful curiosity or opportunistic experimentation and became a course of conduct over an extended period of time.

“The offences seem to have been fueled by the young person’s access to pornography over the internet,” Ms Fryar said.

“In this technological age the dangers of such influences on our children are ever present and require parents to be vigilant about what their children are accessing online.

“Somehow that did not seem to happen here.”

Impact statements from the victims' parents, some read out in court, revealed a “family tragedy of mammoth proportions”, Ms Fryar said.

“The abuse of trust involved was also a significant and aggravating factor,” she said.

“These young girls, his cousins, trusted him, as did all the adults in the family, as an older brother figure.

“It is not putting it too dramatically in my view to say that as a result of these offences the fabric of the entire extended family has been torn apart.”