An inquest into the deaths of two children murdered by their father at their Perth home has heard police took almost three-and-a-half hours to attend after their mother raised the alarm.

Key points: Anatoria Takiwa went to police after her ex-partner rang her with a warning

Anatoria Takiwa went to police after her ex-partner rang her with a warning She attended a station at 6:49pm but police arrived at the house after 10pm

She attended a station at 6:49pm but police arrived at the house after 10pm Jason Headland is serving life in jail with a 31-year minimum for the murders

Three-year-old Andreas and five-year-old Zaraiyah-Lily were drugged and killed by their father Jason Craig Headland.

He put crushed antihistamine into their fruit juice before murdering them, probably by asphyxiation, his murder trial was told.

Their mother, Anatoria Takiwa, had ended her relationship with him in the week before the murders in October 2016.

An ominous warning

She was staying with her parents at the time, while the children were staying with Headland's parents.

On the night of the murders, Headland rang her to pass on an ominous warning:

"I'm going to hurt you … I'm going to break your heart into 50 million pieces … say goodbye to your kids," he said

Jason Headland's marriage broke up a week before he murdered his children. ( Facebook: Jason Craig Headland )

Ms Takiwa called police, who went to the house in the northern Perth suburb of Yanchep and discovered the bodies of the two children.

Headland was also at the house with self-inflicted stab wounds.

He was convicted of two counts of murder and is serving a life jail sentence with a 31-year minimum term.

Police found the bodies of the children at the house after their mother raised the alarm. ( ABC News: Briana Shepherd )

An inquest into their deaths has been told Ms Takiwa attended Joondalup Police Station at 6.49pm on the night her children were murdered, after receiving the disturbing phone call.

But officers did not arrive at the family home until 10.17pm, by which time the children were dead.

'What's done is done'

Giving evidence to the inquest, Ms Takiwa said she had been with Headland on the day of the murders, attending a hospital appointment for Andreas.

Anatoria Takiwa warned police she thought her two children were in danger. ( Facebook: Anatoria Takiwa )

She was due to return to the family home with him and the children after the appointment but began to feel uneasy as they drove back, and instead made Headland drop her in Joondalup.

"He shook my hand and said 'what's done is done'," she said.

"I just thought he had accepted our separation."

She said some weeks before the murders, Headland had spoken of a father who had murdered his children in South Australia by driving off a jetty with them in the back of a car.

"He said to me 'is that what you want me to do?'" she said.

Despite this, Ms Takiwa said she did not believe Headland would harm their children, but had gone to the police station because she was worried and felt uncomfortable.

Call gave friend 'goosebumps'

Family friend Katie Cheeseman told the inquest she was with Ms Headland when she received the call from her estranged husband and was worried about the safety of the children.

"At that time I got goosebumps. I just froze," Ms Cheeseman said.

"Parents shouldn't say things like that. I was thinking, 'he's going to do something very bad'."

Anatoria Takiwa's two children Zaraiyah-Lily and Andreas were killed by her ex-husband. ( Facebook: Anatoria Takiwa )

Ms Cheeseman drove with Ms Takiwa to Clarkson Police Station, but it was closed so they went to Joondalup.

After reporting the threats, a police officer suggested calling Headland, but Ms Cheeseman said they should not do so "because there's mental illness running in the family and he's made threats and I don't think that's a good idea".

Police instead rang Headland's father, Doug, who had previously been looking after the children.

Ms Cheeseman said she and Ms Takiwa were told by police the children were with their grandfather and were safe.

The inquest is examining what time police should have gone to the house to check on the children's welfare. ( ABC News: Robert koenig-Luck )

They were told police would conduct a welfare check on the children within the hour and would call Ms Takiwa after they had done so.

"After we left the police station, I honestly thought everything would be fine," Ms Cheeseman said.

But police recruit Georgina Kennelly — who dealt with Ms Takiwa and Ms Cheeseman when they attended the police station — testified that she told the women Headland had the children and was going to bring them into the station.

She said neither woman objected to the plan.

She did not know of the threats Headland had previously made to Ms Takiwa, nor that he had placed his hands around her throat some weeks beforehand and pushed her.

She said she spoke to Headland by phone when he rang Ms Takiwa while she was at the station and he sounded calm and composed.

The conversation "didn't make me think, 'oh he's done something to the children'," she said.

Nonetheless, she was uncomfortable about the situation and said "something didn't sit right", especially when she noticed Headland had not come into the station.

Confusion over where children were

Earlier, counsel assisting the coroner Toby Bishop told the court police had spoken to Doug Headland, who told them the children were not with him and were probably with his son at his Yanchep home.

Police then spoke with Headland at 7:22pm and arranged for him to attend the police station with the children within 20 minutes.

Zaraiyah-Lily and her brother were given fruit juice laced with crushed antihistamine before they were murdered. ( Facebook: Anatoria Takiwa )

Ms Cheeseman told the inquest she was unaware of the arrangement, and she and Ms Takiwa had left the station because they had been assured the children were safe with their grandparents.

When Headland failed to arrive at the station by 8:20pm, Mr Bishop told the court officers began to make inquiries and tried to call him, but he did not pick up.

It was only after phoning Ms Takiwa at 9:08pm that they obtained Headland's home address.

"This was the first time police were aware of this address," Mr Bishop told the court.

He said the focus of the inquest was on what time police should have gone to check on the children's welfare, and whether it was reasonable to rely on Headland's promise to bring the children to the station.

The inquest is being heard by Coroner Sarah Linton.