Two knives found on the ground near the mother are being tested for DNA evidence.
Police are not revealing the nature of the injuries.
Police are waiting on autopsy results expected to be completed within the next 24 to 48 hours to determine the cause of death, he said.
Supt Morgan said it is now believed the deaths could have occurred as far back as Tuesday.
"Given there was some serious decomposition of the bodies, we'd probably put it between Tuesday afternoon and Thursday lunchtime," he said.
Police have established the mother did not have any known contact with anyone after Tuesday afternoon.
Supt Morgan said there were no suspects yet.
He said the children had different fathers, neither of whom are suspects.
He urged any witnesses to contact police.
-AAP