Criminal investigation branch detectives and scenes of crime officers are at the scene.
Neighbours are being interviewed.
Acting Inspector Geoff Marsh said the man phoned police to report the incident.
He said they were not looking for any further suspects.
“All evidence suggests that the couple were home alone, their children were at school,” Acting Inspector Marsh said.
“The children are being cared for by neighbours.
“They’re shortly to be taken by the police to the child protection and investigation unit at Cairns police station where elder siblings are to arrive from out of town to take care of them.”