Australian Prime Minister Tony Abbott Friday described the killing of eight children in Cairns city as an "unspeakable crime" and expressed grief over the incident.Eight children, aged between 18 months to 15 years, were found stabbed to death at a house Friday.The tragic incident took place at Murray Street in the suburb of Manoora, Cairns Post reported."All parents would feel a gut-wrenching sadness at what has happened," the statement said, adding: "These are trying days for our country. Tonight, there will be tears and prayers for these children."