Now the boy, who was 13 months old at the time, will never walk again, police say.

On Wednesday, a man, 25, charged with the assault, appeared in court for the first time and was formally refused bail.

A woman, who said she was the child's godmother, said the severe brain and spinal injuries caused by the vicious assault had left the toddler in hospital for at least two months.

"He will never walk again, he's in a wheelchair, he's actually with a carer at the moment and he will be with his Dad soon hopefully," the woman, who gave her first name as Taylor, said.

"He will never be the same kid as he was before, ever," she said.

The woman said the child's mother was sticking by her de facto partner, even though he was charged with the assault.

She said the little boy had improved but would never be the same again.

"[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.

"He's doing a lot better than what he was. He's smiling, he's starting to eat little things like biccies and things like that."

Child Abuse Squad detectives allege the man beat the 13-month-old boy so badly on February 20  that he was covered in bruises and went into cardiac arrest.

"Doctors have told police the boy had been shaken vigorously and suffered other injuries, causing damage to his brain, spinal cord and eyes, as well as a cardiac arrest," a NSW Police spokeswoman said.

The boy will be confined to a wheelchair, and will require high-need care for the rest of his life, police said.

Police arrested the man on Tuesday and will allege he is also involved in the supply of the drugs ice and ecstasy.

Officers attached to Strike Force Racemosa raided the man's house in western Sydney and allegedly found drugs and number of items they believe were stolen.

The man was charged with causing grievous bodily harm with intent and the ongoing supply of prohibited drugs.

On Wednesday, he appeared briefly before Blacktown Local Court where he did not apply for bail and it was formally refused.

The Child Abuse Squad comprises detectives who are specially trained to investigate crimes against children, including sexual assault, physical abuse and serious cases of neglect.

Anyone with concerns about suspected child abuse or exploitation should call Crime Stoppers on 1800 333 000.

Reports can also be made to the Child Protection Helpline on 132 111