How can kids so young be so mean??!

My eldest daughter is 8.5. She is very quiet and very shy until she gets to know a person. She has quite a few friends, all kids with similar personalities, so she thankfully has no problems making friends. Unfortunately, due to her personality and that she won't fight back, she does seem to be a target of the mean kids at times. She is also a little bit overweight. Not, overly but she is at the age now where kids are starting to be mean and they are noticing that she isn't stick thin. So it begins, the body image stuff..I was hoping that wouldn't be an issue for a few more years.There are a small group of girls in her class that have said mean things to her and just been generally nasty to her a few times. I had spoken to their teacher about them to let her know what is happening and to keep and eye on the situation. The last incident was just before the school holidays. It was the last day of school and the class was watching the movie Casper. These girls were giggling amongst themselves and my daughter over heard one of them say " Fatso is [My daughter's name] favourite ghost because he looks like her!" My daughter didn't say anything to her teacher but she was clearly quite upset about it when I picked her up from school and she told me what they said. The next day, I spoke to my daughter's teacher about this and she said she would have a talk to the girls about being kinder etc. So, until today, she hasn't had any more problems with these girls.I get a call from my daughter's teacher asking if I could come an pick her up as there had been an incident and she was really upset and wanting to come home. I get up to the school and my daughter was still upset and clearly had been for a while. Speaking to her teacher and the school principal, the same 3 girls had left a note on my daughter's desk which had the words "Stupid fat retarrd" (spelled like this). My poor daughter, even though she must have been so hurt didn't even tell the teacher although had the foresight to keep the note, most likely to bring home to show me. As if that wasn't bad enough, later on in the playground one of the girls pinched my daughter so hard on the arm that it broke the skin! One of my daughter's friends went and told the teacher on duty. My daughter was crying obviously and almost inconsolable. Her friend also told her teacher about the note and my daughter showed her. I am so fucking angry that my daughter who hasn't got a mean bone in her body could be The target of such nasty and mean spirited kids! The school are dealing with it and have been really good, but I just want to personally give these nasty little bitches an attitude adjustment. I know I can't and they are just kids. Kids who may be going through a lot at home. How else do kids so young be so mean??Now, I'm worried that if I don't try to help my daughter be more assertive and resilient, it is only going to get worse as she gets older. She is is just so quiet, shy and sensitive. How do I do this? My younger daughter on the other hand is the complete opposite -extroverted, loud, confident and popular with her peers. My other daughter sees this, which must make her feel even worse. I just feel so bad for her.Edit: sorry it's so long! via /r/Parenting https://ift.tt/2Z8aCjV