I'm seeing a lot of "kids being kids" messages here, which is odd, because yes, we were all kids and we all did stupid stuff, but I'm assuming we were all smart enough to not taunt flying cameras with spinny blades?
To address a few of the questions I saw:
1) The pond is shared, community (HOA) property. My property abuts the pond. So I'm taking pictures of the pond (and the trees, and the sky) almost 100% from my property. Sometimes I venture out, but during the day, when I have time to practice before work, I don't really have a large VLOS slice of the sky, so I just practice in the backyard, and it's a good way to get in drone flying practice and take fun pictures.
2) There is no expectation of privacy in public locations, but I'm also a semi-considerate photographer. I am NOT hovering over people, or near people. The kids were down by the edge of the pond, and my drone was 20 feet AGL (probably 30 feet above their ground level) over my property. The kid's got a heck of a throwing arm, though!
3) I didn't call the police this time, because I didn't want to be viewed as one of those "get off my lawn, ya' damned kids!" Even though I'm at that age where I have the propensity to say that, I don't. My house has a 9' buffer on that side (minimum allowed by law), so what looks like my property is not. Not a big deal.
4) I have cameras on the front and back door, for security, but I don't (yet) have cameras overseeing the front driveway and side yard (facing the pond). I've considered getting those, as it would help me track comings and goings. Again, the pond is public/shared/HOA property and my property is my own, so I can put cameras anywhere I like, facing any direction I'd like. I might end up installing a pond-facing camera at some point, but my drone does a pretty good job when it's up in the air.
5) I once had someone in the neighborhood on the Nextdoor app go off on me because I have cameras on my entryway doors, and sometimes I'll run out (staying on my property) and take pictures of people and vehicles that might be causing damage (or who might be trespassing - the pond is for the exclusive use of HOA members and there are signs all over the place). One time, we had "ding dong dashers" where the kids run up and ring the doorbell then run away. I have a daytime/nighttime camera with very bright IR lights and IR sensitive camera, so I have a seven-day rolling full-HD history of everything that happens at my front and back door. Neighbors were sharing pictures and video (on YouTube) of the culprits. This crazy guy ended up going down the "if you're taking pictures or video of children [even in public] you're a pedophile" road and I was like "WTF!?" So, I try to choose what I share on Nextdoor carefully, because there are some nutjobs out there. (Come to find out later that he's a well-known nutjob in the neighborhood, disliked by most, so I wasn't his first random nutjob target.) To summarize: taking pictures of kids in public is not illegal. At least not in the U.S. Wouldn't want to do that without permission around a kids' park or a school, but those aren't really considered "public" and I'm a considerate photographer, who'd ask a parent for permission first. But in public spaces, we have a general "right of panorama" and NO legal expectation of privacy unless explicitly stated - usually with a sign and a fence. Taking pictures of kids playing at the HOA pond, whether intentional or incidental (I'm not really a fan of taking pictures of most people, so most of my pictures of people are incidental, like "damnit, there's a kid in the shot, can't use that one.")
Anyway.... I appreciate everyone sharing their opinions, legal dealings with the FAA and police, and their own stories in general. The main reason why I posted was, obviously, to find out if anyone else had experienced this type of crap with kids, what they'd done about it, and if it was successful.
I have an annual calendar with small squares, and one of my "do it every day" dots is "fly the drone." It's up there with "four glasses of water," "read," "eat a healthy meal," and "exercise." Even if I only fly a single battery of my Mavic Air every day, it's good practice. So I don't want some kids ruining my practice over my own property by intentionally tossing rocks at my aircraft, and also at my house. It really sucks.