Former residents of Salvation Army boys' homes were subjected to widespread physical and sexual abuse by peers and employees, the Royal Commission into Institutional Responses to Child Sexual Abuse has heard.

The commission has returned to Adelaide to examine four Salvation Army-run homes in South Australia, Victoria and Western Australia.

The Eden Park Boys' Home at Wistow in South Australia, the Box Hill and Bayswater Boys' homes in Victoria and the Hollywood Children's Village at Nedlands in Western Australia will form the basis of the inquiry.

In her opening address, counsel assisting the commission Sophie David said evidence would be heard from 13 former residents of the institutions who would speak of "the traumatic sexual and physical abuse they endured while living there and the impact these experiences have had on them and their families".

She said the royal commission had identified 20 perpetrators of child sexual abuse at the homes as well as a number of unidentified perpetrators and peer-on-peer child abuse.

"We expect the survivor evidence and documentary evidence to show sexual abuse was widespread, unchecked and continued over a long period of time at the Salvation Army institutes," Ms David said.

She said the witnesses would also detail the harsh conditions and physical punishment they were subjected to at the homes.

The commission heard boys were sent to a small room known as the "lockup" for punishment at Eden Park.

Three former residents of Eden Park will give evidence at the hearing, six from Box Hill, three from Bayswater and one from Nedlands.

The commission heard some victims who later came forward to seek compensation from the Salvation Army felt they were treated like a number rather than a person.

Former Eden Park Boys' Home resident Graham Rundle earlier said the next fortnight would be an important step in many victims' journey.

Boys were 'punished' when reporting abuse, commission told

Ms David said some of the victims never reported the abuse at the time because they felt it was "pointless" and they would not be believed.

"A number of the former residents of the institutions will give evidence that they did not tell anyone about the sexual abuse that they suffered at the time it was occurring because they were fearful that they might be physically punished or they thought they would not be believed," she said.

"Some former residents will give evidence that they reported their abuse to officers who were in charge of the homes.

"Some residents will give evidence that they were physically punished or subjected to further sexual abuse by the person to whom they reported the abuse.

"Others say no action was taken at all or that they had no-one to tell."

She said one victim who had been abused by other boys at the Eden Park Boys' Home was then raped by a Salvation Army officer when he reported the abuse to him.

The commission heard another victim at the Bayswater Boys' Home had reported sexual abuse to another Salvation Army officer who punished him by placing him in a fire escape for two or three nights.

Ms David said the Salvation Army was aware of the allegations of child sexual abuse in each of the operations.

"It is expected that documents will be tendered which show that the Salvation Army knew of child sexual abuse occurring at each of the institutions at the time they were in operation," she said.

"The adequacy of the Salvation Army's response will be considered in light of the Salvation Army's own policies and procedures."

Salvation Army knew of Eden Park abuse as early as 1940s

Records revealed that the Salvation Army knew about sexual abuse at Eden Park as early as the 1940s, the commission heard.

Ms David said from 1995 until the end of last year the Salvation Army had received more than 400 reports of child sexual abuse.

"In total, the Salvation Army, from January 1, 1995 until 31 December, 2014 has received 418 claims relating to child sexual abuse and paid a total of nearly $18 million to former residents of Salvation Army operated institutions," she said.

She said the Salvation Army had issued several public apologies for the sexual abuse of children by officers and employees at the homes.

She said there had also been more developments in policies since a Victorian parliamentary inquiry.

"Since 2013 the Salvation Army has implemented numerous policy changes and training in relation to child protection, responding to allegations of child sexual abuse, integrity checks and social program policies," Ms David said.

A number of criminal prosecutions had also been brought against Salvation Army officers, but some criminal investigations were ongoing, the commission heard.

The commission will sit in Adelaide for the next fortnight, before delivering its findings at a later date.

The commission has previously heard about sexual abuse and cover-ups at the Salvation Army's Eastern Territory, and found that the organisation failed to protect young boys from abuse.