Yeh it’s unacceptable, parents should keep a close watch on their children and regularly check in. Know who their friends are, what’s happening at school etc.
I myself was bullied at home until adulthood and it impacts a child immensely. I remember being bullied at the age of 10 aswell and it wasn’t even severe but it upset me terribly. Children can be so sensitive, they need love care and attention.
Parents shouldn’t have children if they can’t take up the responsibility of taking an active interest in them and give them the attention that they need.