The bodies of twin two-year-old girls, a three-and-a-half-year-old girl, their mother and their grandmother were all found in a Coode Street, Bedford property yesterday.
The ages of the children and their relationship to the two adult women found at a Bedford home in Perth's east were confirmed on Monday by WA Police.
"The man now assisting police remains in custody", a police statement said, adding "no charges have been laid at this time".
"The homicide squad now have teams of detectives on the ground, accompanied by specialist forensic police who are meticulously working their way through this crime scene".
Assistant commissioner Paul Steel told local media: "Police have located the bodies of a number of deceased people including women and children. It does send a ripple through the community of Western Australia", Mr Steele said. They were acting on information received by a man who went into the rural police station of Karratha earlier in the day.
Five people were found dead in a suburb of Perth, Australia, police said.
Police said there are no ongoing safety concerns for the community.
Shortly after giving birth to her first daughter, Mara fell pregnant with twins, and the pair settled at their Bedford home with their children Charlotte, Alice and Beatrix.
No charges have been laid yet and it is unclear whether the man is related to the victims.
"The WA Police Force will continue to apply our efforts to this matter as a priority, and the Homicide Squad will ensure a professional and meticulous investigation is undertaken", said a police statement.
"It's just so sad, they've got primary school aged kids and I thought it just couldn't be", she said.
"It's just horrific on every level".
"It is a awful, bad tragedy for the family", he said.
It has taken everyone by surprise, we are all in complete shock.
"The scene has not yet been forensically examined so the exact number of adults and children is actually unknown to me", Steel said.
The tragedy comes after a 19-year-old man was charged with murdering an eight-year-old boy, a 15-year-old girl and their mother at Ellenbrook in July.