A lack of visibility between rooms in older children's hospitals posed an abuse risk to patients, a federal inquiry has heard.

The Royal Commission into Institutional Responses to Child Sexual Abuse has heard how a young girl, known as AWI, was repeatedly molested by a Royal Children’s Hospital Melbourne volunteer behind the closed door of a children’s ward playroom in 1981.

The abuse, by volunteer Harry Pueschel, continued for a five-month period.

Pueschel was eventually sacked in 1998, but returned as an auxiliary staff member and was caught lying his way back into a ward.

The hospital’s chief executive officer Christine Kilpatrick says older hospitals did not conform to modern architectural design aimed at making wards more transparent and visible.

But she says the current hospital, built in 2011, meets safety standards with inpatient wards made predominantly of glass.

She also said there are now strict measures for hiring volunteers.

“I can certainly say the former Royal Children’s Hospital didn’t conform to those safety requirements,” Prof Kilpatrick said.

“Visibility is a critical – an absolutely critical issue, and, with that, a culture of patient safety amongst our staff and volunteers.”

Prof Kilpatrick said some of the circumstances that lead to AWI being sexually abused could not be repeated today, because the playroom walls are now made totally from glass, are highly visible and without curtains.