By Agence France-Presse
Police said they responded to an early-morning phone call and arrived to find a "horrific incident" in the small town of Osmington near the world-renowned wine-growing region, south of Perth.
Five bodies were found inside a house and two outside. Homicide detectives were investigating but police were not looking for a suspect -- suggesting a murder-suicide.
"I can only say at this point in time, we have no information to raise concern about wider public safety issues," Western Australia police commissioner Chris Dawson said.
"We're still yet to make contact with other members of the family so at this point in time, all I'll confirm is that there are four children and three adults that have all been located deceased."
The ages of the children were not released.
Dawson said there appeared to be gunshot wounds, "but I don't want to go further than that as two firearms have been located at the scene".
"The loss of any life is tragic but four children and three adults, this is a significant tragedy," he said.
Mass shootings are not common in Australia, which has strict gun laws.