WARNING: This story contains details and content that some readers may find distressing.

A mother stabbed, strangled and suffocated her three children before burning their bodies in a house fire in the West Australian town of Port Hedland.

Margaret Dale Hawke, 36, formally pleaded guilty at the Supreme Court in Perth on Friday to murdering her 10-year-old daughter and two sons, aged seven and four months.

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They died in July last year in the family's Port Hedland home, sending shockwaves through the town of about 16,000 people.

The court heard Hawke strangled her daughter with an electrical cord and stabbed her eight times in her chest and heart.

Her seven-year-old son was found with three stab wounds to his chest and wounds on his neck from also being strangled.

Hawke admitted smothering her infant son before setting her home alight and walking into the street as it was engulfed by flames.

Prosecutor Justin Whalley SC told the court one witness described her as "really calm" as she watched it burn.

Another heard her say: "He's taken everything from me".

Whalley said Hawke then screamed and cried, saying: "My babies, my babies … You don't have to suffer any more."

Members of the public tried to enter the home and save the children but it was too dangerous.

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She told police she didn't know of any other way to help her children before admitting to lighting the fire.

"My three babies … I hurt my babies. I did it to my babies," she said.

Firefighters put out the blaze.

Hawke's elder son's body was found on a mattress in a room at the front of the property.

Her daughter and other son were found in a room at the back of it.

Hawke was taken to hospital, where she later admitted to staff she had murdered her children.

"I don't know why I did what I did. Maybe to stop the pain in all of us," the court heard she told police in an interview after the incident.

Whalley said Hawke told the children she loved them and asked for their forgiveness before murdering her daughter, followed by her sons.

He said an arson investigation found the fire was deliberately lit with two ignition points in the house.

None of the children were found with soot in their respiratory systems indicating they likely died before the fire was lit.

In court on Friday, Hawke was overcome with grief.

She sobbed in the dock and repeatedly banged her head on a balustrade until security staff stopped her.

Judge Michael Lundberg listened to sentencing submissions before adjourning his sentencing decision until May 5.

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WARNING: Aboriginal and Torres Strait Islander readers are advised this story contains images of a person who is deceased.

A Perth teenager who hurled a concrete block at a car, fatally injuring a pregnant mother has been sentenced to five years in detention but with time served could be released in less than two years.

Noongar woman Diane Miller's family screamed out in grief and anger in court over the sentence handed down on Friday.

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The 17-year-old boy, who cannot be named for legal reasons, pleaded guilty to unlawfully killing Miller, 30, in December last year.

He admitted lying in wait behind a wall after a car park melee involving weapons on November 29 and throwing a 1.9-kilogram brick at a car.

It flew through the passenger side window and hit Miller, who was five months' pregnant, in the head, causing catastrophic injuries.

She died in hospital, along with her unborn child, amid an outpouring of anguish in the Noongar community.

The teen, who was initially charged with murder before agreeing to plead guilty to the lesser offence of manslaughter, fled before handing himself in to police shortly after.

Miller's family wept and vented their anger in Perth Children's Court as Judge Hylton Quail read the facts of the "tragic" incident.

"You were impulsive … You didn't stop to think if it was a bad idea," he told the boy.

"You persisted with the plan to use the rock."

Quail said the boy's traumatic life and brain damage contributed to his decision to throw the lump of concrete.

He also accepted the teen was genuinely remorseful and cooperated with police.

However, he said Miller was an innocent and blameless victim of a cowardly act.

"Most significantly she had a baby and was 20 weeks' pregnant," Quail said.

"You took her life and deprived baby Lloyd of his mother and you deprived Ms Miller's unborn child of life.

"You will have to live with the consequences for the rest of your life."

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Quail read Miller's mother, Annette Miller's, victim impact statement to the court.

She said her daughter, affectionately known as "Dinosaur" by family, was her pride and joy.

"I had to grieve twice as much because I not only lost my daughter but also my unborn grandchild," she said.

Quail sentenced the boy to five years' detention at Banksia Hill Juvenile Detention Centre and he must serve a minimum 26 months before applying for supervised release.

With time served he could be released in about 21 months or opt to be transferred to an adult facility when he turns 18

Quail acknowledged the difficulties the teen had faced in the facility and would continue to endure, including unlawful 20-hour lockdowns due to staff shortages and threats from other inmates.

He also said he had witnessed a member of Miller's family threaten the boy in court on Thursday during sentencing submission.

After the sentence was handed down Miller's family's anger boiled over as they were ushered away by security.

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Outside, Miller's brother Malcolm Clifton said he was outraged by the sentence and the teenager should have also been punished for the death of his sister's unborn child.

"There's justice for you, what a load of bulls— … I'm sick to the guts with the law system … He should have got 15 so he can think about what he's done," he said.

"He knew what he was doing when he picked up the brick.

"Everyone knows what they are doing when they pick up a weapon.

"They intend to use the f—— thing."

Miller's sister, Alison Miller, described her as a beautiful soul.

"She was harmless … Everyone has got to fight this," she said.

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Football superstar Sam Kerr will carry Australia's flag at the upcoming coronation of King Charles III.

Prime Minister Anthony Albanese announced on Friday afternoon the Matildas captain, who is currently playing for her London-based club side Chelsea, will be the flagbearer for the event on May 6.

"The prime minister will join the governor-general, state governors and a number of other Australian representatives (at the coronation), including Ms Sam Kerr OAM who will be the Australian flagbearer," a statement from Albanese's office said.

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Kerr holds the record as Australia's leading international goalscorer of all time, and has finished third in voting for the Ballon d'Or – a prestigious player of the year award – in the past two years.

She was awarded an Order of Australia for her service to football in 2022.

https://twitter.com/TheMatildas/status/1651820122624131077

Kerr is one of 14 Australian representatives for the coronation, a list that includes musician Nick Cave, comedian Adam Hills, doctor and Street Side Medics founder Daniel Nour, and Victoria Cross recipient Daniel Keighran.

In addition to naming Kerr as flagbearer, Albanese announced his trip for the coronation will include a meeting with UK counterpart Rishi Sunak and a visit to the shipyard where the first of the British AUKUS submarines will be built.

"I'm honoured to represent Australia at the coronation of the King and the Queen Consort, a historic occasion," Albanese said.

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"I am proud to join a group of remarkable Australians who will also attend the coronation, showcasing our truly diverse and dynamic nation.

"This will be the third occasion that I meet with Prime Minister Sunak.

"We will discuss the Australia-United Kingdom Free Trade Agreement, which will shortly enter into force, and will deliver benefits for Australian exporters, Australian workers and our economy more broadly.

"I will meet with the highly trained and skilled workers at the Barrow-in-Furness shipyard, who will be an important part of helping Australia acquire nuclear-powered submarines through AUKUS."

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