A man who was "a hostel parent" at a home for wards of the state 40 years ago has been found guilty of sexually abusing eight of the children entrusted into his care.

Martin James Cooper, 66, had been on trial in the Perth District Court for the past four weeks on 43 charges dating back to between 1978 and 1983, when he and his wife Nancy were the cottage parents at the Warminda hostel in East Victoria Park.

There were eight complainants — four boys and four girls aged between 11 and 16 — who were continually subjected to intimidation, threats and repeated physical and sexual abuse.

They were all wards of the state and while the building was owned by the State Government, the hostel was sponsored by the Uniting Church.

The jury deliberated for almost five days before finding Cooper guilty of 30 charges including rape and indecent dealing.

Cooper was also convicted of procuring two boys to molest one of the girls in the back of a car while he watched on, and then raping the girl himself.

Cooper was in a position of authority over children at the Warminda Hostel in the Perth suburb of East Victoria Park. ( ABC News: West Matteeussen )

He was found not guilty of the other 13 charges, including an allegation he abused a friend of one of the girl's who was staying overnight at the hostel.

Jail term inevitable, judge tells abuser

Cooper was charged in 2016 after three of the complainants took their cases to the Royal Commission into Institutional Responses to Child Sexual Abuse.

That led to a police investigation, and Cooper being extradited to Western Australia from the eastern states to face trial.

He denied all of the allegations.

After the verdicts, Cooper's lawyer, David McKenzie, applied for his client to be released on bail, telling the court he suffered from early onset dementia as well as other physical health problems.

Judge Mark Herron refused the application, saying the offences were very serious and it was inevitable Cooper would receive a jail term when he is sentenced next week.

Cooper is the second person to be convicted of abusing children at Warminda.

In September 2015, former counsellor Allan Keith Huggins was sentenced to more than nine years' jail for abusing seven boys in the early 1990s when Warminda was run as "a community support hostel".