Homicide squad detectives are investigating after a three-year-old boy was found stabbed to death in a southwest Sydney home, as a 45-year-old man recovers in hospital.

Police found the body of the boy at the Riverwood unit about 4pm on Wednesday, after responding to a “concern for welfare” call.

The man, who was also in the apartment with critical injuries, remains under police guard in hospital.

He was treated at the scene, but was in a stable condition after surgery.

Superintendent Sheridan Waldau said the apartment complex was now a crime scene.

“The Homicide Squad has been contacted and they are now on the scene and assisting us with those inquiries,” she said on Wednesday.

Supt Waldau said the attack on the child appeared to be a “horrific” domestic violence-related incident.

Police believe the mother of the boy died a few years ago and that the child was living with the man and another female family member, who called police.

The man has a partner and she is also helping police.

“Any kind of incident involving a small child is always a tragic incident and our condolences go out to the family of the child,” Supt Waldau said.

“Unfortunately, police attend domestic violence incidents all the time.

“We attend 140,000 incidents every year, and unfortunately some of them end up in homicides.”

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