Misanthropic Malignancy

I just got back from the elementary school playground, and there are no words to properly express my rage. There were two of us: mothers, each with two children, each with one who was well under the age of two. That wasn't the problem, though. The problem was the pack (for lack of a better word) of 14-16 year-old kids (pretty evenly divided guy/girl) running around the open space next to the playscape, playing some variation on tag. As Joseph and I moved off toward the swings, the teens converged on the playscape climbing over, under and on top of the equipment. Elena was still playing in the rocks beneath them, until their play started to get rough and she came to join us. Then they started throwing rocks. These were not soft lobs, either. I saw at least four of them throwing handfuls of rocks, full force, in all directions. Handfuls of rocks are like buckshot, though--you're bound to hit something. And, indeed, the ricochets kept getting closer and closer to the six of us who had taken refuge at the swings. I was livid. "All of you!" (yes, I shouted, but it's the same shout the police use to quell riots) "No more rocks!" Did this stop them? No. They had the nerve to move to the other side of the play scape and continue on, as if the extra five feet would buffer us from their stupidity. We were trapped on the swings, and Joseph was wiggling to get down. We couldn't even leave because they were between me and the stroller. And thus, I snapped. I didn't threaten, because I had no real authority over them, but I so wanted to use their cell phones to call every one of their mothers and ask why they had lost the basic social manners that my 4-6 year-old nieces and nephews can handle just fine. One of them protested that it was a public park so I couldn't kick them out. Since when has "public" meant "I can do whatever I want and you can't do anything about it," though? And what about me? All I wanted was to let my children play without being scared for their safety. I tolerated the rough play and climbing on top of things, but I draw the line at projectiles. Furious and unable to let my children play anywhere near them, I left. And then the ringleader told me to have a nice day. Please, tell me we're raising our children to be better than this! I do my best, but it's hard not to feel defeated when faced with this sort of thing.