The "profound injuries" suffered by a 27-day-old baby boy meant a decision on whether to turn off life support would be made quickly, Department of Child Protection director general Terry Murphy said today.
Mr Murphy said he would make the decision after consulting with doctors and the boy's family, including his 16-year-old mother.
The boy was allegedly assaulted by his teenage father in a Bunbury hospital room when the baby's mother left briefly to get some food.
Mr Murphy said today that there was no indication that the alleged assault could have been predicted.
He said the boy's father had unrestricted access to his son during visiting hours, along with the mother.
The case had been overseen by 30 midwives since the boy's birth.
"With 30 midwives observation, and the family's observation, the parents cared for the child looked after the child fed the child," Mr Murphy said.
"There was no indication during that time that such an alleged event could occur."
Mr Murphy said the boy's father had been a frequent visitor to the hospital and had been involved in his feeding and care.
But he said that he was "very troubled" and had been in the care of the department since he was 12 when he was abandoned by his mother.
"This is a boy that had a troubled history. But once again there was nothing in that history that led our skilled experienced departmental officers, working with the family, and the hospital and other agencies who were involved with this family.. To predict this event," he said.
Child Protection Minister Helen Morton said it was a "terrible terrible situation" for the baby, his family and those who had worked with the family to try and make it a "successful outcome" for the family.
She said it was still unclear what had happened to cause the baby's serious injuries.
She said a lot of work had been put in to enable the baby to go home with his mother.
"From the day the baby was born he was a regular visitor he was involved in the feeding and the baby's management," she said.
"The arrangements around him visiting through visiting hours.. was agreed to jointly by the DCP and the family and hospital staff."
Last night Mrs Morton said she had asked for an investigation into the "distressing and tragic incident" after police charged the baby's 15-year-old father with aggravated grievous bodily harm.
Mrs Morton said the Department for Child Protection had been extensively involved with the family since the baby's birth and they had been provided with the "appropriate support and services".
The 27-day-old boy was supposed to be getting out of hospital for the first time yesterday since his premature birth last month.
He is instead on life support in Princess Margaret Hospital with critical head injuries after he was found injured on Saturday.
The West Australian believes that the boy's 16-year-old mother returned to the room about 7.20pm to find the baby unresponsive and the father claiming to be trying to give him CPR.
It is unclear exactly how he was injured but homicide detectives and forensic officers have spent time at Bunbury Hospital, where the baby had been cared for since his birth last month.
It is believed his Perth-based mother had returned to her home town of Bunbury for her son's birth in order to have the support of her immediate family.
Mrs Morton said the baby was now in the care of DCP and its chief executive Terry Murphy was responsible for making decisions regarding his medical care.
"I have asked Mr Murphy to work with the police, the hospital and all relevant government departments to review the circumstances and events leading to this incident," Mrs Morton said.
The 15-year-old, who Mrs Morton said was under the care of the State, appeared in Bunbury Children's Court via video link from Banksia Hill detention centre yesterday.
Magistrate Elizabeth Hamilton read the charge of aggravated grievous bodily harm to the accused, who said he understood the charge.
He was remanded in custody to reappear in court on February 28.
The baby's mother posted on Facebook yesterday: "I hope my son is okay.
"Missing him so much. Just want him in my arms."