What Would You Do?

The scene: Sandbox at local indoor playground.
The kids: two young boys, one around 5 or 6 ("Big"), one around 3 or 4 ("Little").
The parents: My friend and I, unrelated to the boys in question, are only parents in the immediate vicinity. Herd of moms standing several yards away, chatting. None immediately identifiable as belonging to the boys.
The Situation: Big and Little are playing next to each other at the sand table. Little is coming too close to Big's pile of sand. Big head-butts Little, hard. Friend and I gasp. No response from the herd. Another head-butt. A third. Finally, Little hits Big back. There's a short scuffle, with both boys landing blows. Big starts wailing "Moooooom! He hit me!" A blond woman swoops in, and starts to whisk Little away from the table, hissing "that's it! You cannot play here anymore!"

So, what would you do in this situation? Would you have stepped in when the fight first broke out? Would you have ignored the whole incident?

I, for one, always hesitate to discipline a kid I don't know. But in this case, the big kid was really whaling on the little one, and it didn't look like anyone else was going to break it up. And then, when a mom finally responded, she knew that Little had been hitting, but not that he'd only been defending himself. Ultimately, I ended up touching the mom's sleeve, and quietly telling her "the other boy was headbutting your son." She answers "actually, they're both mine. I thought I was watching them, but I guess they never tell you the whole story." We exchange mild pleasantries about brothers and sibling rivalry. She still doesn't say anything to Big, but she sets Little down and he wanders away.

Ok, story over, right? Nobody seemed offended and nobody seemed mad. But not five minutes later, I hear this mom telling her friend what had happened, in tones that were definitely sneering. Both agreed it was weird and rude that I'd intervened. Leaving alone the fact that these woman were talking about me when I was standing mere inches away from them (apparently, they think I'm deaf?), I'm wondering, did I really do anything wrong? What, if anything, should I have done in that situation?

I guess I could have stayed silent, and maybe I should have. But I know that if M were in that kind of situation, I'd rather have another mom fill me in on what really happened than punish my kid for defending herself. I wasn't trying to be confrontational or judgmental, I was just trying to give the mom information that seemed relevant to me. But was I out of line, anyway?

(coincidentally, I had planned on writing a post today about how I fear I'm becoming a "sanctimommy." Not that that's any way related to the question at hand. But I'll probably try to discuss that tomorrow).