The deaths of two South Australian children at the hands of their mother's partner could have been prevented had they been taken from her care when an older sibling was removed over fears for his safety, an inquest has been told.
Deputy Coroner Anthony Schapel has opened an inquiry into the deaths Korey Lee Mitchell, five, and his six-year-old sister Amber Rose Rigney.
They were strangled by their mother's partner at a property north of Adelaide in May 2016.
Steven Graham Peet is serving a 36-year non-parole period after pleading guilty to killing both the children and their mother, Adeline Yvette Wilson-Rigney, in May 2016.
In his opening address on Tuesday, counsel assisting Ahura Kalali told Mr Schapel that before the murders another child of Ms Wilson-Rigney had been removed from her care because he was deemed to be in a situation of serious danger.
"(His) death had no doubt been prevented not because of the unforeseeable risks posed by Peet, but due to the foreseeable risks of harm if he continued to reside with his mother," Mr Kalali said.
"So why then were not Amber and Korey removed too?
"Had Amber and Korey been removed from the care of their mother, their deaths would also have been prevented."
Mr Kalali also told the inquest that two Families SA staff had called at the home where the children were killed, north of Adelaide, just three hours before police were called and the three bodies were found.
They knocked on the door, got no answer and could not see anyone inside, so had left.
He also outlined the long history of abuse, care and neglect notifications to authorities over the care of the three children, particularly the oldest boy.
Mr Kalali said the inquest would focus on the response by child welfare authorities to information related to the risk and potential risks to all three children.
The hearing continues.
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