More than 1500 people have reportedly been sexually assaulted or harassed in mental health wards across Australia over the past six years.

Among them is 13-year-old girl Florence (not her real name) who was allegedly raped at Perth Children's Hospital last year, ABC News reports.

She says she was assaulted in a mental health ward by another patient, while medical staff gathered in a nearby nurse's station.

"Knowing I'm not the only one genuinely shatters me," she wrote in an essay about her experience.

"We were supposed to be protected."

Earlier in the day the perpetrator - a 13-year-old boy - allegedly told Florence he was going to "do stuff" to her that night.

"I was just frozen, knowing he was so much larger than me," she said.

Perth Children's Hospital provided Florence's family with a heavily redacted copy of a clinical incident review commissioned by WA's Child and Adolescent Health Service (CAHS).

It found the nursing staff on duty that night did not do their required hourly checks between 12.30am and 3.30am.

The review also said CCTV captured vision of the boy crawling across the ward floor into Florence's room about 12.30am.

Florence's parents said they were told the nurses were afraid of the boy but they did not call the hospital's security team for help.

The family is now considering legal action against the hospital over the incident.

ABC Investigations used freedom of information applications and publicly available data to establish the number of people assaulted in mental health wards.

It said the full extent of the problem remained unclear because there was no nationally consistent definition of such incidents and the data provided by state health departments was inconsistent.

Privacy laws also restrict the media from accessing hospital information.

CAHS said it conducted a review after the alleged incident involving Florence and the Office of the Chief Psychiatrist and the Mental Health Advocacy Service undertook two independent investigations.

"We can confirm that immediate and comprehensive support was provided to those involved and referrals were made to relevant authorities," chief executive Valerie Jovanovic said in a statement to AAP on Tuesday.

"We have taken this very seriously."

CAHS said $7.7 million had been allocated to make changes to the ward, including structural changes and some reconfiguration, to improve its layout.

"I want to reassure families that patient safety remains our highest priority," Ms Jovanovic said.

WA Police have been contacted for comment.

Lifeline 13 11 14

beyondblue 1300 22 4636

Kids Helpline 1800 55 1800 (for people aged 5 to 25)

1800 RESPECT (1800 737 732)

National Sexual Abuse and Redress Support Service 1800 211 028