While the boy's statement could have been a joke or could have been taken out of context, you're absolutely right in thinking, "It could have been important." I would rather lay the information in the hands of a parent now, giving them the opportunity to check out the situation and intervene with the help of professionals, than to hear six months later that the kid was in "a world of hurt," perhaps quite literally.
I really don't think the mother's reaction is surprising. It's unfortunate, especially in her treatment of you, but not surprising. She may have reacted out of fear: What if it's true? Or, perhaps her response came out of utter frustration: I can't deal anymore! When people are afraid or frustrated, the messenger of potentially bad news is usually the first to feel their sting.
Just remember that her reaction was hers. I'm sure her response had little to do with you, if anything at all, and a whole lot to do with what she was feeling inside. After all, a different parent (or even this same woman under different circumstances) might have thanked you or expressed concern about the situation with her son.
I can understand why you are feeling misunderstood. You acted out of concern, and you received an emotional slap in the face. Focus on your intent, Julia. You wanted to help a kid. You wanted to warn a mom about a potentially serious situation. Those are good things, Julia. They are very good things. I can't tell you how many times I've heard a parent say, "I just wish I would have known..."
((((Julia))))
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