Anyway, I was sort of half watching them when I saw the little guy throw a rock at my daughter's head. I could tell she wasn't hurt because he didn't "throw" very hard, but still. His mom didn't see and I hesitated a moment. I don't like to hover and intervene too much, but preventing my little girl from being pelted with stones seemed like the parental thing to do.
However, before I had a chance to say anything, she raised her hand and said firmly in a calm, clear voice, "No. Don't hit me."
Her friend blinked, and dropped the second rock he had picked up, and they went back to playing peacefully. No correction or intervention needed.
I was surprised that she handled it that well on her own. But I think this was good.