So I'm 22 and I walk my little sister home everyday. as I walked her home I noticed that a group of siblings walk home together as well one of the little girls and my little sister's class. Her older brother probably about four years older was calling her names and being mean to her as she cried. I didn't think too much about it other than sibling fighting cuz me and my brother used to fight about the same way. But then her brother starts dragging her down the street calling her chubby and stupid and then starts chucking rocks at her she's crying and I tell him to knock it off but he doesn't listen and they go back into their home. What would you do in this situation? Who do you address? I've seen their mom baby the older brother and the youngest sister before but the middle child who is being bullied seems to be ignored and I'm not too sure what to do about it.