A former Marist Brothers principal was "not sure" as late as 1989 that committing a sex act against a child was a crime, the Royal Commission into Institutional Responses to Child Sexual Abuse heard on Monday.

John Holdsworth, who left the order in 1999, also told the commission he could not even be sure he was aware adults could and sometimes did act in a sexually predatory way against children.

Commission chairwoman Justice Jennifer Coate had asked: "In 1989, you did or did not know that children were at risk of adults behaving in a sexual way towards them?"

Mr Holdsworth, who had been the headmaster at a north Queensland school where Sutton had taught in the mid-1970s, thought for a moment before replying: "I really can't put a time line to it [when he became aware that could happen]."

Justice Coate asked Mr Holdsworth if he had watched television or read newspapers at this point.