But roughly halfway through the five-hour trip, their auto broke down.
"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", he said.
Initially located were a 19-year-old man, a 19-year-old woman and a three-year-old boy, described as a young family.
Remnants of food and water were also discovered at the scene.
They never made it that far.
Police said the alarm had been raised by a man who entered a health clinic in Willowra on Wednesday.
The searing heat reached 40C at the start of the week in Willowra and 38C on Wednesday before dropping off in the past few days.
The couple's vehicle broke down roughly halfway through their journey.
Nobbs said police still couldn't rule out the possibility that there had been other passengers in the auto when it broke down.
The search was set to continue until police were able to completely rule out that there weren't other people in the vehicle.
Police said the deaths are not being treated as suspicious and ruled out a auto crash, but they are investigating whether it was heat-related.
Because of flooding rain and the remoteness of the area, investigators took a few hours to reach the vehicle.
"One of the avenues we are looking at is that they have walked off from a vehicle in extreme weather and may have got caught out", superintendent Shaun Gill told the Australian broadcaster ABC.
Police said the deaths are a "tragic situation" and are not being treated as suspicious.
"At this point, we hold grave concerns for the welfare of this child", superintendent Jody Nobbs told reporters Thursday.
"This does serve unfortunately as a timely reminder for anybody traveling on the Northern Territory roads to ensure that, when you do travel, your vehicle is in a fit state to travel".