The 32-year-old woman has been charged with murder after the body of a four-year-old boy was found alone inside the Wyong home, on the NSW Central Coast, on Saturday afternoon.
The boy had significant arm injuries, but police have yet to confirm whether these were the cause of death.
Welfare concerns were first raised after the woman took herself to the local police station and spoke with officers, Superintendent Chad Gillies said.
"Through those conversations, police formed genuine concerns and that's what triggered our response," he told reporters on Sunday.
"It was an extremely confronting scene."
The child was yet to be formally identified, but investigators believe he lived alone at the unit with the woman.
She was known to police and detectives were not looking for anyone else in relation to the boy's death, Supt Gillies said.
The woman was charged on Sunday with domestic violence-related murder.
A number of items of property have been seized for forensic testing, including the car that the woman used to drive to the police station.
Officers were still examining the property on Sunday morning.
"Whenever a child is a victim of violent crime and whenever a child is (allegedly) murdered, it strikes at the core of community," Supt Gillies said.
The woman was refused bail to appear before court later in the day.
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