This is experienced mostly in school-aged children.
When I was a kid, I was never bullied by my friends or classmates.
My eldest child was bullied by his classmates, he reported it to me.
That report triggers me to approach their school discipline department and I reported it together with my son.
Since the report, the child who bullied my son was called and heard his side.
Then, his parents were called for a meeting with me and were told of the incident.
From then on, no incident again happened re: bullying.