The officer then told the boy to "show some f**king respect."
Police released the boy just minutes after the incident, according to his mother.
The boy's 21-year-old sister says the police officer should have sat her brother down and tried to talk instead of hitting him.
His mum revealed he had previously been charged with robbery and assault.
Following the incident, the officer has since been charged with assault which has pleased the boy's mother.
"I hope it prevents him from hitting someone else. I don't hit my kids," she told CBC.
Experts have sided with the boy's mother, despite the 12-year-old's disgusting behaviour, saying the officer had no right to hit the child.
"The kid, from what I saw, is unarmed and is not representing any imminent threat to the arresting officer or the arresting officer's partner and efforts should have been made to de-escalate, particularly with someone of that age," Ian Scott, former director of the Special Investigations Unit said.
An Idaho police chief also said when responding to a call of a child acting out, an officer's job is to de-escalate the situation, not inflame it.