What seems little to us, as adults, is huge to kids.
My DD had an experience in second grade when she was the one that was excluded. A little girl on the cheerleading team passed out gum to everybody except DD. when DD held her hand out for her piece, the girl had one piece left so instead of giving it to DD, she kept it for herself. DDs feelings were hurt and she let the words fly, "I hate you!"
The next day, at the bus stop, the girl's mother confronted me that my DD had hurt the feelings of her DD with her words. My response to the mother was that both girls were wrong. Her DD excluded mine which resulted in my DD saying what she said. I agree that what my DD said was hurtful, the other mother did not agree that excluding mine was hurtful as well. I told the mother I would talk to DD, and I did.
Later, the other mother wanted to get our girls together to play, but, my DD didn't have any desire to play with this girl. I completely supported her choice. After all, following the incident involving the gum, I told DD that she has to be kind to others but she doesn't have to be friends with somebody who treats her badly.
To this day, that instruction has stood the test of time. DD is not a "victim" of the mean girls. She is also not a mean girl herself. The other girl, who years ago excluded mine, is now firmly in the mean girl clique. She has, herself been the target of exclusion at times, but was never taught that she has the power to turn her back on people that treat her that way. She continues to desire inclusion in this group.
Lol, I know this because, believe it or not, her mother and I are friends, our girls are kind to each other, and mine has, on occasion, stood up for hers. But they still are not "friends"...meaning they are not in the same crowd. And I'm ok with that.