Police hold man.
The baby's 27-year-old mother also underwent surgery late Wednesday for stab wounds to her neck, and was in a serious condition.
Police in the eastern Australian city of Brisbane were called on Wednesday to an apartment complex where they found the two injured and a five-year-old boy, a two-year-old girl, and a four-month-old girl dead from stab wounds.
A man in his 30s was found a short distance from the apartment with what were believed to be self-inflicted stab wounds, police said. Police were guarding the man in hospital.