The 15-year-old father accused of fatally bashing his premature infant son is receiving legal and psychological assistance from authorities, it emerged today.

Police are considering whether to upgrade a charge laid against the boy, who is accused of assaulting his month-old son at Bunbury Regional Hospital.

He has been charged with aggravated grievous bodily harm.

The baby died in his mother's arms in hospital yesterday, just over a week after he was allegedly assaulted.

The premature boy was on life support at Princess Margaret Hospital and had been taken into State care after receiving critical head injuries.

The Department for Child Protection said it had not needed to make a decision about switching off the baby's life support because he had died naturally.

Relatives of the infant, who had not left hospital since his birth in January, were by his bedside when he died yesterday afternoon.

Department for Child Protection director general Terry Murphy said the WA coroner and ombudsman would investigate the cause of death, and review the circumstances and events that led to it.

Mr Murphy said he was also determined the accused boy would still be treated like a “human being” despite the shocking allegations against him.

“The father remains in state care, I am his guardian and therefore I have arranged legal representation for him,” Mr Murphy told ABC radio today.

“Psychological support for him at the moment is also critical.

“He is charged with horrendous crimes, but he is a still a young person with his own history of serious damage. He still needs to be treated like a human being.”

His 16-year-old mother posted her thoughts on Facebook last night, saying she would love her son "so much forever nd always".

"So hurt nd lost man what am ganna do nw withowt my baby son am notinq," she said.

"Rip My Son Atleast Yuh Went In My Arms."

Mr Murphy last night offered his condolences to the newborn's family.

"I would like to express my sadness at this tragic loss and offer my sincerest condolences to all members of the family," he said.

"I ask everyone to please be aware of the sensitivities and needs of the family and respect their privacy at this difficult time.

"The department is continuing to work with the family and is providing appropriate support services."

Mr Murphy said the Coroner and the Ombudsman would now investigate the cause of the boy's death and review the circumstances and events that preceded the tragedy.

Child Protection Minister Helen Morton also expressed her sympathy for the family.

"I am saddened to hear the tragic news that the baby boy injured in Bunbury last weekend has now passed away," she said.

"The department continues to work with the family and is providing the support services to help them at this very difficult time."