What would you do?

Yesterday, I took my son to Chick-fil-a (if you don't know what that is, it's only the best fast food place ever.)  Any how he was in the play area with a bunch of kids, all whom we did not know.  There was about 4 or 5 older kids, ages 7-9 I would guess, and then a group of kids  ages 3-5.  Now this one boy was a little on the smaller side, but boy was he something.  He kept throwing stuff at the older kids who would then through it back at him.  I was keeping an eye out, becuase I knew what was coming and didn't want my son involved.  Pretty soon the little boy decided it was time to go running to Mom, and sure enough he told his Mom loud enough for me to hear, that the big kids were throwing stuff at him, and bothering him.  Now here is the part I was uncomfortable with, the Mom asked me, if things were getting out of hand in there.  Mind you , I am watching this through the glass,  I told her yes, things were getting a bit rough in there.  But what I wanted to say was your kid is the one causing the problems! But I didn't, and she went and yelled at the big kids, who blamed her son, who denied it.  See where this going?  Somebody is a big time trouble maker who's momma thinks he does know wrong!  Would you step in?  Should I have said something?  I didn't want to get in the middle of it~somehow I don't the child had ever been told he did wrong~
This went on for awhile~ the kids would start playing, and the little "monster" would go running to his mom, who would come tell everyone to stop bothering her little boy.  Never once realizing that maybe, just maybe there was more to his little story.
Aren't children amazing?  Aren't Mom's amazing? wink, wink~ so what would you do? Seriously, to get involved or keep minding your own business? 
We left as soon as I could convince my son it was time to leave, and honestly I probably will never see these people again (hope she's not a reader of mine), but isn't it amazing how parents and kids act!