Mr Wilson said the boy turned to his mother and said, "Mum, she just hit me," before standing between his mother and grandmother for protection.
Rimene continued to abuse the boy, walked over to him, grabbed him and shoved him against the wall of the bank.
She then punched him a second time, on the arm. As a result of the punches, the boy received a reddened upper arm.
Mr Wilson said Rimene continued her verbal tirade towards the boy and said: "I am going to kill you, I know what you look like."
The boy's mother grabbed the child and moved him to safety, telling Rimene, "He is only 7 years old."
Rimene shouted more threats and then walked away along Queen St towards Church St as police were called, Mr Wilson said.
Soon afterwards, Rimene was located on Church St and arrested. As she was being put into the patrol car, she turned to the boy's mother who was nearby and said: "I know your son's face and I'm going to slit his throat when I see him again."
Police said Rimene admitted everything, said she "hated white children", and repeated her threat to kill the boy if she ever saw him again.
Mr Wilson said the boy and his family were "extremely shaken up" by the incident.
He said the victim's family had never seen Rimene before but were worried that she could carry out her threats.
In sentencing, Judge Ian Mill said Rimene was "not very well at the time".
"But you should not have done what you did. You should not have assaulted the boy and you should not have threatened him."
Rimene was given a suspended sentence, which means if she offends within the next six months she could face resentencing on the original charges.