The couple's sons, then aged six and three, saw their dad assault their mum and started crying, so she urged them into the next room, away from the violence.

Four years ago, the same police officer arrived  at his wife's home - they were separated - to pick up his son for karate training.

His wife had mentioned in a phone message the boys had been misbehaving, so when he arrived he walked straight into his son's room.

His wife followed and saw her husband with his hands around their son's neck. He threw the 13-year-old him onto the bed, and "slapped him around".

This officer, who was a senior constable with Victoria Police until he quit last year, was originally committed to stand trial on 11 family violence-related charges. On Wednesday he pleaded guilty to two.

The case raises serious questions about how the powerful police union decides which members it will back in court.

The Police Association has paid all of his legal fees, through a contested committal in the Magistrate's Court to pre-trial argument and Wednesday's plea in the County Court.

"All the members I have spoken to have been absolutely disgusted that their membership fees are going to support men who bash their families," the ex-wife, herself a former police employee, said outside court on Wednesday.

In a statement, Police Association secretary Ron Iddles said each legal case was different and judged on its circumstances. Support stops when a member pleads guilty, he said.

If the offence occurred while an officer was off duty, they must demonstrate the charges were laid solely because they were a police officer, he said.

The officer's two assaults were set against a background of family violence, prosecutor David Cordy told Judge Richard Smith.

"The offences your honour is required to sentence could not be seen as isolated or one-off acts and it could not be said there was no subsequent misbehaviour."

The officer's former wife, who cannot be named, read her victim statement in court and said the damage from the assaults and his denials would never leave her or their children.

"The anxiety, stress and fear you subjected our boys to continues and has impacted their lives enormously," she said

In a statement, one of her sons said he never enjoyed spending time with his father because he was always worried something would happen. "I was always scared he would get angry and hit me like he has done".

The former senior constable joined the police force in 1990 and worked  at stations across Melbourne, defence barrister Dermot Dann QC told the court.

He was of "good character" and served the community as a police officer for 28 years, Mr Dann said.

After working as an officer on the scene of a number of fatal incidents he later developed post traumatic stress disorder. He also had anxiety and depression, the court heard.

He went on sick leave and eventually was placed on an emergency services pension of about $61,000 a year in 2013. He remains on it today. The case was adjourned until May 25 for further plea and sentencing.

After a number of high-profile public cases that pinpointed police failings, including the murders of 11-year-old Luke Batty and Point Cook woman Kelly Thompson, Victoria Police has taken a strong public stand against domestic violence.

But when the police officer's former wife asked for help from Victoria Police before her husband was charged she got little response, she said outside court.

"The whole process has been appalling and he has all the rights," she said.

For family violence help call Safe Steps: 1800 015 188