Tyler was shot and shot and then died after his mother allegedly pulled a gun on him while he was playing with her three dogs.
Tyler, 11 and his brother Alexander, 7, died of gunshot wounds to the head.
The family said they were on their way to their home when they were confronted by a man in a black Toyota SUV who demanded they drop their three dogs in the car.
They said they tried to calm him down, but he continued to demand they take the dogs.
The children were then shot in the head, the children’s grandfather said.
“I was trying to calm the guy down, and I guess he was just trying to scare him,” he said.
The elder Hamilton said he tried to call the police and they responded but couldn’t do anything.
He said they also called the emergency services.
“They didn’t have a name for the police,” he told AAP.
Police arrived but could not get in contact with the family because the children were playing in the driveway, Mr Hamilton said.
He said when the family went into their bedroom, they saw Tyler lying on the floor with a gunshot wound to his head.
“He was lying on his back,” he added.
A spokesman for the Adelaide Coroner’s Court said he was waiting for an autopsy to be completed.
Mr Hamilton said Tyler had three other dogs with him.
Tyling died on Sunday after the dogs were put in a crate and put in the trunk of the SUV.
His mother, Mary Hamilton, 24, was charged with aggravated murder, causing grievous bodily harm and leaving the scene of a fatal accident.
She is due to appear in Adelaide Magistrates Court on Tuesday.
Ms Hamilton pleaded not guilty to three counts of aggravated murder.
Her barrister, Richard Faucher, said Ms Hamilton had been a troubled person and her children’s grandmother had said she had “an evil streak”.
“The fact that she was in the care of the authorities is a terrible tragedy, she is not capable of being rehabilitated and she is responsible for her actions,” Mr Fauchers told the court.
Family friends said the Hamiltons had two young daughters and a son.
Tyler was shot at his grandmother’s home in Adelaide’s east in October.
Mrs Hamilton is believed to have fled to Queensland after the shooting and her husband was later arrested.
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