The Herald on Sunday first reported the charges in June last year but the full details could not be revealed until today.
Judge Denise Clark said the man's most significant offence was the assault on the baby.
Court documents revealed the details of the vicious attack that left the 9-month-old hospitalised with lacerations around his mouth, welts on both sides of his head, multiple cheekbone fractures, a torn bottom lip and tongue and facial grazes.
His eyelids were so swollen that the baby could barely open them.
The assault happened on the morning of February 19 last year.
The man's then-partner was cooking breakfast and he took the baby into the bedroom after becoming frustrated with his continual grizzling - the result of teething.
Alone in the room, the man struck the baby repeatedly on his face and head and grabbed him by the chin and mouth to stifle his cries.
He then forced something solid in the infant's mouth causing a tear between his tongue and base of his mouth.
From the next room the baby's mother could hear her partner say: "f*** up, shut up you little c***".
She threatened to call the police as the attack on the baby continued.
Her partner then turned on her, threatening to burn her with a hot pan before pushing her towards the ground and kicking her legs, hip and shoulder.
As she lay on the ground, he then fetched the baby and demanded she feed him.
Family members arrived shortly after and sought medical help for the baby after noticing bruises on his face.
He lied, telling them an internal door had fallen on the baby.
The baby spent a week in hospital and was then placed in the care of Oranga Tamariki.
At sentencing Judge Clark revealed the man had also assaulted the mother of his children on multiple occasions between September and October 2015 - including while she was pregnant.
On one occasion he hit her so hard with a game console that she could not open her eye.
Another time he went up behind her and held a knife firmly to her throat.
On a third occasion the woman's sister tried to defend her and the man threw her to the ground then straddled her while jamming his thumbs in her eyes.
The court heard the assaults happened when the man was drunk and at a time when the relationship was facing significant difficulties.
"That does not excuse your behaviour, but it provides context for it," Judge Clark said.
The Crown sought a prison sentence for the man, starting at three years.
However after giving him credit for remorse and the promise of employment, she sentenced him to home detention and ordered him to complete 160 hours of community work.
"It does seem to me with right environment you are able to behave in quite un-obstructive ways," she told him.
"This is a long sentence for you, but it is a sentence that allows you to address the needs you do have."
The maternal family of the injured infant were shocked when they heard the result.
His grandfather told the Herald that his family had been "failed" by the court.
"If my daughter hadn't stopped him, he could have killed my grandson," he said.
"Home detention - this is a joke, a huge joke.
"There has been no justice for my grandson whatsoever - it's a slap on the hand, they might as well have given him a cup of tea and a big piece of cake as well.
"We were expecting a jail term - I'm not happy at all."
He said his grandson, who remained in state care with his younger brother as a result of the attack by his own father, had recovered physically but would bear emotional scars forever.
"He's quite a violent little fellow - he throws things, he wants to punch," the grandfather explained.
"He's got a hard road ahead, that poor little boy, he'll remember that assault for life - he won't forget it.
"That little boy is going to suffer for the rest of his life."
The grandfather sees his grandchildren once a week and has been working to get his daughter into a better place in life so they can get custody back.
The incident and aftermath had a "huge" impact on his family.
"After this, I couldn't sleep," he said.
"I'm just always worried… when I walked into that hospital room and saw (the baby) it didn't even look like him.
"I just dropped to my knees and shed so many tears.
"Now the person who did this to him gets to be at his own home, see his family when he wants, eat what he wants - when my grandson is missing out.
"He's missing out because this fellow did what he did… this feels like egg on our faces.
"I feel let down, there's been no justice whatsoever - it's just not right."
He was also angry that the offender could not be named publicly.
Under the Criminal Procedure Act young victims of crime cannot be identified in the media.
This means the baby's father's name cannot be published.
"Why should he get to hide? We don't want any of this kept secret," the grandfather said.
The Herald has contacted police to see if there is any plan to appeal the sentence.
The sentencing came just days after a 4-month-old baby girl was admitted to Middlemore Hospital with 16 fractures she suffered over a period of time.
New Zealand has the worst rates of child abuse and domestic violence in the developed world - every five-and-a-half weeks a child is killed by a family member and each year more than 90,000 are exposed to violence in their home.
Shine spokeswoman Holly Carrington was shocked by the case.
"Nine months home detention and community work seem a totally inadequate sentence," she said.
Victim advocate Ruth Money called on police to "immediately" appeal the "weak" sentence.
"What planet is this judge on?
"It's bad enough that he hit an adult, but to do what he did to a baby and get sentenced to home detention is absolutely atrocious.
"No wonder we have such a bad child abuse rate in New Zealand - this is an epidemic and it is being enabled by judges giving such weak sentences.
"This is disgraceful and I call on the Crown to appeal this immediately."
DO YOU NEED HELP?
If the child or young person is in immediate danger, call police on 111.
Otherwise, contact your local police station for help or advice. Click here for locations and contact details.
If you're worried about a child you are urged to contact Oranga Tamariki immediately on 0508 326 459; or email contact@mvcot.govt.nz.
