Sorry, I didn’t realize that “I was just following orders” has now countermanded common human decency. I’ll keep that in mind, that there are some mindless robots on the job.
What if the cops got there, heard the story, laughed at the 12 year old, and left the house without arresting the grandmother. Then an hour later the 12 year old is dead. I'm telling you that does happens in domestic scenarios (usually when a husband gets even angrier at his wife for calling the cops). So many departments have said "you MUST arrest" in domestic situations. If only to remove the abuser so they can settle down.