Margaret Dale Hawke, 36, pleaded guilty to three counts of murder after killing her 10-year-old daughter and two sons, aged seven and four months, in the family's Port Hedland home in July last year.
She was sentenced for the three killings and and one count of criminal damage by fire on Friday in the Supreme Court in Perth.
Justice Michael Lundberg said Hawke had breached the most fundamental duty of a parent and brutally killed her children.
The court heard Hawke strangled her daughter with an electrical cord and stabbed her eight times in her chest and heart.
She also strangled and stabbed her seven-year-old son. He was found with three stab wounds to his chest and wounds on his neck.
Hawke tried to drown her infant son but failed and instead smothered the child before walking to a beach where she disposed of the knife.
After she returned to the family home where her dead children lay, she lit two fires and walked out into the street as it was engulfed by flames.
A witness described her as "really calm" as she watched it burn.
Another heard her say: "He's taken everything from me".
Hawke then screamed and cried, saying: "My babies, my babies ... You don't have to suffer anymore".
Members of the public tried to enter the home and save the children but it was too dangerous.
Hawke 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 the blaze out. 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.
Hawke was taken to hospital and later admitted she had murdered her children.
"I don't know why I did what I did. Maybe to stop the pain in all of us," she told police in an interview after the incident, the court previously heard.
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 died before the fire was lit.
She was sentenced to two years and eight months' jail for the arson, to be served concurrently.
1800 RESPECT (1800 737 732)
Lifeline 13 11 14
