Queensland Police said the vehicle carrying six people rolled into Wyaralong Dam on Beaudesert Boonah Road this afternoon.
“Another child was airlifted to hospital in a critical condition while a fourth child was treated on scene,” Queensland Police said in statement.
“A man and a woman have also been transported to hospital.”
Police say preliminary information suggests the car lost control and crashed into the dam.
“The car was submerged in the water for a period of time before the six occupants, two adults and four children, were recovered by emergency services and witnesses,” the statement said.
“Two children were pronounced deceased at the scene.”
Queensland Ambulance said paramedics as well as critical care crews and rescue helicopters were called to the scene.
Police divers and the Forensic Crash Unit are also in attendance.
Police have closed the road in both directions and have urged motorists to avoid the area.