The boy was the only survivor of the horror crash, when the vehicle the group was in crashed along a ridge line and into an embankment at Gundy, 20kms east of Scone.
Rescuers described the embankment, at the northern end of Gundy, near Timor, as a cliff.
Police were unable to confirm how far the car went down the embankment.
The crash is believed to have occurred sometime on Monday morning while the boy, his father, aged in his 40s from Sydney, and his grandfather, aged in his 70s from Brisbane, along with the property owner were inspecting the Waverley Rd lot.
The three generations of the family involved are believed to have travelled from Sydney to inspect the farm.
Police said all occupants were ejected from the vehicle, believed to be a four-wheel drive, killing the three men and leaving the boy with a broken arm and other injuries.
After concerns were raised by family members — when the group did not return — a neighbouring landowner came across the tragic scene with the young boy only metres from his dead father and grandfather.
Two Westpac Rescue Helicopters were dispatched from Newcastle and Tamworth with the Tamworth chopper arriving first to find there was nothing they could do for the men. The second helicopter was then called off.
Paramedics could only access the remote a site by quad bikes.
The boy was flown to Scone Hospital before he was taken to John Hunter Hospital, in Newcastle, by ambulance.
He is in a stable condition, believed to be with loved ones by his bedside as the family deals with the heartbreaking loss of a father and son witnessed by the boy.
Due to remote and rugged nature of the property, police suspended their crime scene investigations on Monday night and will resume investigations on Tuesday.