I would add to these classics,
Little Girls Can be Mean, which is particularly targeted at parents (and girls) ages 5-12 or so. In this age group, bullying is less likely to be done with an intent to wound, and more likely to be due to not understanding (or at least not thinking about) the perspective of the other person. There is an interesting scenario where they describe how one girl is bullying another and talk about how to support her. Then in the next chapter, they talk about the same scenario, as seen by the other girl - and now it looks like
she is the victim of a bully!