Survivors of physical and sexual abuse in orphanages and children's homes across Australia will be in Perth to support men giving evidence at a hearing into Christian Brothers-run residences in Western Australia.

The hearing, beginning on Monday at the Western Australian Industrial Relations Commission, is the 11th case study by the royal commission examining how Australian institutions responded to child sexual abuse. It is the first hearing in WA.

The evidence from men who were resident at Castledare Junior Orphanage, St Vincent's Orphanage Clontarf, St Mary's Agricultural School at Tardun and the notorious Bindoon Farm School/Boys Town, an isolated institution north of Perth, is expected to be some of the most shocking and explosive heard by the commission.

The hearing will run for two weeks.

Thousands of children, some as young as five, were sent to Australia as part of various British child migrant schemes in the 40s and 50s, with many housed at Bindoon which opened in 1938.

Many of the child migrants were told they were orphans only to discover years later that they were not. Some of those will join a rally outside the commission hearing.

Leonie Sheedy, co-founder of support and advocacy organisation Care Leavers Australia Network (CLAN) said a fortnight of early morning rallies would be held.

"It is time for the Christian Brothers to be made accountable for the rapes, floggings, cruelty, neglect, brutality, child slave labour, inhumane treatment and lack of education of boys in their care," Ms Sheedy said.

The rallies were being held to make the general public aware of the criminal treatment of the boys, she said.

The Christian Brothers had a lot to answer for, as well as their maltreatment of child migrants "they were raping Aussie boys in the 1920s", Ms Sheedy said.

CLAN members will attend the hearings to offer support to witnesses, she said.

The Perth inquiry will investigate the responses of the Christian Brothers and relevant Western Australian State authorities to the abuse allegations at the residences.

It will also look at the experience of people who went through the Catholic Church's Towards Healing process, Redress WA, civil action and/or directly to the Christian Brothers for compensation or assistance.

Archbishop of Perth Timothy Costelloe last week published an open letter in which he reiterated his full support for the work of the commission.

In his letter he expressed "horror and deep shame" at what happened and asked forgiveness from those whose lives had been badly damaged.