Gus Lamont was last seen by his grandmother playing at the Oak Park Station homestead in outback South Australia on September 27.
Police on February 5 declared someone living at the remote station was a suspect in Gus' disappearance and likely death.
They have confirmed the boy's grandparents, his mother and his younger brother were at the property at the time he disappeared but stressed his parents were not suspects.
On Monday, police announced that officers had returned to the sheep station, 45km south of Yunta in the state's Mid North, to continue searching for evidence, and would remain in the area for at least the next two days.
Detective Superintendent Darren Fielke previously said that a person who lived at the station had withdrawn co-operation in the investigation after "a number of inconsistencies and discrepancies" were identified in the information they provided.
Gus's grandparents Josie and Shannon Murray released a brief statement via their lawyers earlier in February in response to the police allegations.
"We are absolutely devastated by the media release of SAPOL Major Crime," they said.
"The family has co-operated fully with the investigation and want nothing more than to find Gus and reunite him with his mum and dad."
Initial searches were based on Gus walking off the station and becoming lost, but the case was later declared a major crime.
The two other investigation options were focused on the preschooler being abducted or whether someone known to him was involved in his disappearance and suspected death.
"We don't believe now that Gus is alive," Det Supt Fielke previously said.
Investigators searched the homestead on January 14 and 15, seizing items including a vehicle, a motorcycle and electronic devices for forensic testing.
Det Supt Fielke said ground and aerial searches had failed to locate Gus or any items belonging to him and family members had provided information that police had reviewed.
Gus's disappearance sparked intensive searches spanning almost 500sq km and involving hundreds of police and volunteers as well as  aerial support and mounted units.
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