I'm writing about work

I am feeling terrible right now. It involves some of the kids I work with and some bullying. I knew there was something going on between one boy and one girl, some negative comments and poking fun at. I stepped in whenever I saw it. I asked the girl if she was okay. I put the boy on time out, called his mom, had him apologize. No matter what I do, he doesn't seem to care. The thing is, I still like this boy. I don't think he's a bad kid. No kid is bad.
Sometimes the girl would tell me of an incident several days later. She seemed annoyed, and yet okay. She told her mom about it today, and her mom was very angry and upset, not with me, but upset just the same. I listened mostly and explained what I see and do. I encouraged her to write the principal (her idea), because that way she could express her anger in a constructive manner. I feel like I could have done something sooner. I feel like I should have stepped in sooner. I only have a small inkling of that deeply protective mothering instinct. There were even tears in her eyes. I told her it hurts me when I hear the negative remarks, too, because it does. I didn't really know what to say. I just feel bad.