The bodies of two adults, both 19, and their three-year-old son were found late on Wednesday on a remote road near Willowra, about 300 kilometres north of Alice Springs in the Northern Territory.
The body of a 12-year-old boy has been found after a desperate search in a remote part of the Outback.
At a press conference on Thursday morning, Investigators revealed that a major land and air search is now underway for another child who they believe may have also been in the vehicle.
The bodies of a man and a woman, both aged 19, and their three-year-old son were found 4.5km away from their broken-down auto. Authorities initially thought the passengers had died in a auto crash but they now suspect the family died of exposure.
"Although police have no information that suggests there were other passengers in the vehicle, we will continue a precautionary land and air search until we are satisfied that all areas of interest have been sufficiently canvassed", Southern Desert Division Superintendent Jody Nobbs said.
"Although police have no information that suggests there were other passengers in the auto, we will continue a precautionary land and air search until we are satisfied that all areas of interest have been sufficiently canvassed", he said.
The vehicle was found about 70km from Willowra and last seen leaving the indigenous community on Friday bound for Yarra Yarra.
Relatives told authorities a 12-year-old boy had also been travelling with the young family, but he was missing from the scene.
"This is a tragic situation and our thoughts remain with the families affected by this incident", Nobbs said. The three bodies were found about 4.5km from the vehicle.
Police said the alarm had been raised by a man who entered a health clinic in Willowra on Wednesday.
This morning, police said a 12-year-old boy, who they believed was with the group, was not found among the dead.
Police urged anyone with information about the child's whereabouts to contact them immediately.