Days after the federal government formally apologised to the thousands of people who suffered abuse in Australian institutions, ACT Attorney-General Gordon Ramsay tabled a bill that would make it a crime to fail to protect a child from sexual abuse in institutions.

The bill would also tighten up sentencing in historical abuse cases, and enable child sexual offences to be charged as courses of conduct.

The amendments are in response to the recommendations of the Royal Commission into Institutional Child Sexual Abuse, and were foreshadowed in March.

Mr Ramsay said the failure to protect offence would help prevent the "unacceptable failures" exposed through the royal commission where people in authority moved known abusers to different roles in the same institution and allowed them to continue abusing children.

The offence will apply where an adult knows there is a substantial risk another adult involved in the institution will abuse a child, they are in a position to reduce and remove that risk, and they do nothing.

Cases like the Marist Brother's handling of Gregory Sutton and Kostka Chute would fall into this category as there were multiple reports, canonical warnings and admissions of child sexual abuse, the bill's explanatory statement said.

Reporting the behaviour to police or through reportable conduct legislation may not be enough to reduce or remove the risk either.

Amendments in the bill will also allow for the charging of child sexual offences as courses of conduct.

Mr Ramsay said that meant a single charge of sexual intercourse with a young person can be charged by describing a pattern of behaviour over several months.

"A discrete time, place, and allegation for each alleged incident will not be required for the charge," he said.

The royal commission heard that delineating separate acts in cases of persistent abuse was " at best, an artificial exercise that does not convey the nature of the abuse they endured, and, at worst, impossible".

The bill also clarifies that sexual offenders should be charged at current standards, rather than historical standards.

While the ACT's human rights laws say a penalty may not be imposed on anyone for a criminal offence that is heavier than the penalty that applied to the offence when it was committed, the royal commission found historic sentencing standards downplay the long-term psychological harm to victims caused by sexual abuse.

The commission found on average, it took 23.9 years to tell someone about child sexual abuse and in such cases, "it is likely that that offender has benefited from many years of living in freedom in the community - a benefit that may well not have been available if the offender had admitted to the offending and subjected themselves to the criminal justice system at the relevant time".