Crime scene at toddler's NSW home

The family of a toddler fighting for his life in a Sydney hospital have told police one of their two pet dogs knocked the three-year-old over at a park.

Officers are scouring a home in Oberon, in NSW's Central Tablelands, where the boy lived with his stepfather, mother and adult brother.

Police were called to the home on Sunday afternoon where the child was unconscious.

Detective Inspector Luke Rankin said police were told the child was injured after being knocked over by one of the family's dogs.

"That's one of the lines of inquiry we're following up in our investigation," he told the ABC.

The park is across the road from the family's home on Cunynghame Street.

Police are talking to neighbours in the area in an attempt to locate any witnesses, Insp Rankin said.

The stepfather and mother were at Sydney's Westmead Hospital on Monday where the boy is in a critical condition.