Greg Anderson murdered Luke at a Victorian cricket oval during a custody visit in February.
He was covered with blood and holding a knife when he lunged at emergency services workers called to the Tyabb oval, and was shot dead by police.
The inquest into Luke's death has heard the 54-year-old once held up a knife while talking to his son and said: "This could be the one to end it all."
The inquest heard Ms Batty was not told Anderson had failed to appear in court on charges of assault and not answering bail.
She learned that Anderson's housemate sought and was granted an intervention order in January this year through media reports.
Ms Batty said when she saw Anderson at the cricket oval on the night of Luke's death it occurred to her to call the police, but she decided not to.
She said she had previously had unpleasant situations trying to get the police involved at the cricket club.
She said she didn't trust the situation, and previous attempts had been traumatic, stressful and unpredictable.
She said she thought: "This will be the third time I've tried to get this man arrested in front of Luke and his friends at that bloody oval."
The police had Anderson's address, so she thought it would be better if they arrested him there, discretely, Ms Batty told the inquest.
Ms Batty said Anderson was not always violent, but was always controlling.
She cried when she was asked to described her relationship with her son.
"He was everything. He was my only son, my only child," she told the court.
"He was the centre of my life. I made every decision for him.
"I never want anyone to be sitting where I'm sitting."
Ms Batty said Luke began realising his father was different, and once told a school teacher he thought he was the only good thing in his dad's life.
"As he matured he wanted his dad to be like other dads," she said.
But she told the inquest that Luke never believed his father would be violent towards him.
The inquest heard Anderson and Luke were practising in the cricket nets, substantially on their own, when the attack happened at the Tyabb cricket oval on February 12.
Luke died after Anderson struck him with a cricket bat and attacked him with a knife.
An eight-year-old boy saw Anderson raise the bat over his right shoulder but did not see it connect with Luke.
He ran and told his father, who called paramedics.
When emergency services workers arrived they saw Anderson kneeling by Luke.
At first they thought he was helping him, the inquest heard.
Anderson, covered with blood and holding a knife, lunged at police and paramedics.
The 54-year-old was shot by police and said "let me die" as paramedics attempted to treat him, the court heard.
When ambulance workers tried to approach Luke, Anderson said "he's in heaven now".
Anderson died in hospital from gunshot wounds and self-inflicted knife wounds.
