Craig Regan, 25, was charged on Tuesday with causing grievous bodily harm with intent and ongoing supply and possession of the prohibited drugs ice and ecstasy.

He was looking after his de facto partner's 13 month-old son one afternoon in February when he allegedly shook the boy so violently that the baby sustained damage to his brain, spinal cord and eyes and went into cardiac arrest.

Police said the boy, who cannot be identified for legal reasons, will be confined to a wheelchair and will require high-level care for life.

The boy's mother, who has not been charged, said she was sticking by her partner, despite the allegations.

"I don't regret ever leaving him in Craig's care because I trusted him 100 per cent," she told A Current Affair on Thursday night.

"The only doubt that I have is that I wish I never went to work."

She said she received a call at work on February 20 about an emergency at her western Sydney home.

"I was actually following an ambulance on my way home from work and they were making the same turns I would make to come to my house," she said, while crying.

"I seen [sic] the ambulance turn into my street but I still didn't comprehend that it was at my house."

She pulled into her house to see paramedics "on top of my son doing CPR, his body just being thrown around".

The mother, who was not paid to appear on A Current Affair, broke down as she spoke about her "little prince" and said the incident had torn her family apart.

"He would never leave my hip, he was just like my little prince, he was everything," she said. "It's broken me as a person, like, normally I'm pretty strong but ... there's no word that can describe how I feel. Like, it's ripped my world apart, it's torn my family apart."

She disputed the police's assessment that her son would never walk again, saying the little boy was already defying the odds.

"He's already moving parts of his body they said would never move. He's holding his head up like they said he'd never be able to do so he's defying all the odds and doing everything they said he wouldn't do," she said.

The boy is now in foster care and hasn't seen his mother for more than a month.

A woman who said she was the boy's godmother told Fairfax Media on Wednesday that the boy would never walk again and would live with his biological father.

"He will never be the same kid as he was before, ever," the woman said. "[He was] very happy, he started to learn how to walk about two, three weeks beforehand and he will never walk again; he is in a wheelchair," she said.

Mr Regan was refused bail in Blacktown Local Court on Wednesday.