Step 1: take a chill pill
Step 2: see step 1
Anything that’s a problem once isn’t really a problem, if you’re not the responsible party. What are the consequences, to you, of a nuisance for a short amount of time, once in a while? Keep that in mind before acting.
If it’s a recurring problem, then things are different, but perhaps the best approach is to find a new venue where it’s not a problem, because there’s little you’ll be able to do to change things.
The world seems to be full of people just looking for something to be annoyed at and to gripe about. The evidence is obvious: something annoying happens once, and they pop up like mushrooms. Fortunately, they’re the minority, and best politely ignored.
Regarding kids in my house or on my property, it’s another matter. If the “responsible” parent isn’t, I will be, with no apology. They either follow the rules or they’re not permitted on premises. Our son’s friends always knew what the rules were, where the boundaries were, and respected them. Only once did a parent give me grief for chiding her son. It was a very close friend, and well… I let her express her ire and left it at that. Regardless, her kid appreciated the environment we provided.
He’d been fooling around by our winterized pool, and fell in, breaking through the ice (shallow end, fortunately). At age 14, it wasn’t serious, but he did put a big hole in the cover. I probably said something like “Dammit, Jon, you know better!” He now jumps out of helicopters to save peoples’ lives, so between his mother and me we didn’t mess him up too badly. Perhaps it was good practice.