That does suck Nick. My 9yr old had some kids over not that long ago to watch movies at The Plex. Before I started the movie I laid down some rules about running, wrestling, getting up on my speaker stage, etc. I also explained how expensive every thing was, believe me 9 yr olds do understand.
I came down a few times and noticed they started to lose their concentration on the movies and started throwing pillows. I reminded them in a firm, not loud voice that I would shut the movie off if it continued. So, they were good for another 20 minutes or so.
The next time down I noticed one of the kids trying to juggle 3 pool balls, then he proceded to throw one across the room towards another kid standing by one of my m80's. It bounced off my screen, luckily it is a PVC material and didn't hurt anything.
Now, I don't like to raise my voice, but sometimes it is required. I basicaly said in a pretty loud voice, "What did I say?", that was all it took and they behaved the rest of the movie.
I'm not sure how I would handle it if one of my 80's got knocked over. I know one thing, the kids would be going home, and it would be a long time until another showing.
Freaking kids have no respect anymore, or most likely need an a$$ chewing, time outs just don't work.