Officers in the Queensland city of Cairns have also cordoned off the street on which the bodies were found, and said the crime scene will remain in place for at least a day.
The bodies were discovered at an address on Murray Street, a quiet boulevard in the suburb of Manoora. Dozens of police vehicles are at the scene, as investigators continue to search the house and garden for clues.
Expert investigators from Queensland's state capital, Brisbane, have been requisitioned to help local officers.
"As it stands at the moment there's no need for the public to be concerned about this other than it's a tragic event. The situation is well controlled; at the moment there's no concern for anyone else in the environment," said Detective Inspector Bruno Asnicar.
"The crime scene will continue now for probably the next day or two and as we get further information we will share that with you."
Asnicar added: "These events are extremely distressing for everyone of course and police officers aren't immune from that. We're human beings as well.
"However, the police that we have here are very highly trained and professional people and they're going about their job in the way that I would expect them to."
Authorities have confirmed the victims range from 18 months to 15 years old. Local reports suggest all were siblings.
A second woman, has now been admitted to hospital, following the earlier admission of a 34-year-old woman who is thought to be the mother of the murdered children.