Homicide detectives have officially taken over the investigation into the pogo-stick death of a seven-year-old Sydney boy.

The boy was found dead inside his Oatley home, in the city's south, about 6.30am (AEST) on Tuesday.

Members of his family told police he had fallen off a pogo stick the previous day and hit his head in the fall.

Police have been treating the boy's death as suspicious.

The Seven Network has reported that the family is known to the NSW Department of Family and Community Services.

On Friday night, police said the homicide squad had taken over the investigation.

"The investigation is being led by the state crime command homicide squad," a police spokeswoman said.

She said initial post-mortem reports indicated the boy's death was suspicious and inquiries were continuing.