NSW Police Deputy Commissioner Peter McKenna said the use of knives or edged weapons in four alleged domestic violence murders over the weekend was "barbaric".
A woman, aged in her forties, and three young children with stab wounds were found inside a vehicle in the Blue Mountains, west of Sydney, on Sunday afternoon.
One preschool-aged child died at the scene despite witnesses rushing to help, delivering first aid while waiting for emergency services to arrive.
Mr McKenna confirmed the mother is the suspect in the alleged domestic violence homicide.
"We will allege that her condition is the result of self-inflicted wounds," he told reporters on Monday.
"We have to wait for the medical side to play out. Once that has played out, if she recovers from those injuries, our detectives will look to speak to her with the intent on charging with homicide."
Paramedics treated the two surviving children and the mother at the scene before taking them to Westmead Hospital and Westmead Children's Hospital, where they remain in a critical condition.
The stabbings came at the end of a horror weekend across NSW, after three women were allegedly stabbed to death inside their homes within a 12-hour period on Saturday.
Mr McKenna described the past two days as devastating.
"All four scenes were horrific. When you are using knives or edged weapons, in which all four matters we will allege, it's quite barbaric," he said.
"People who stab people, who cut people, it's actually very confronting, and whenever there are children involved, it doesn't get worse than that."
The events that unfolded over the weekend were confronting and incredibly violent, Premier Chris Minns said.
"We can't become numb to the pain or the violence that we see," he said.
"It's profoundly distressing, and I understand why the people of Sydney and NSW are horrified over the last 24 hours."
The Blue Mountains incident took place at a seemingly random location, Mr McKenna said.
"The mother of the children has stopped the vehicle and by the crime scene, it appears that it has happened at that location," he said.
The children's father had been notified hours after the incident and he remains at the hospital with them.
He had been at work when he received the call from police.
Police said the mother was not previously known to them.
NSW Opposition Leader Kellie Sloane said she was "sick and tired" of wake-up calls about domestic violence.
"I've had enough. We need to do something," she told reporters.
"This is something that is not just on the government. It is on all of us.
"There is a sense of betrayal here, that across our country we're being let down, that we are losing good women, mothers, grandmothers, sisters."
Mr McKenna praised the efforts of the "upstanding" members of the public who responded to the tragic scene.
"There were some good Samaritans who came past that scene first and alerted police, and went to the trouble of life-saving techniques with these kids," he said.
Responding officers would not be spared the hardship and would have access to available supports.
Police said the weapon used and the circumstances surrounding the incident would form part of investigations.
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