Given that you know nothing about them, you need to tread very lightly. If they're inconsiderate enough to do that, they could potentially be psychopaths who would do much worse with little provocation. If you're not able to get a read on them, I wouldn't even talk to them about it. Go with the boulders. Five years and no one knows anything about them? Huge red flag IMO.
Take it from me, YOU DO NOT WANT CRAZY NEIGHBORS. You'd be surprised how quickly something trivial can escalate when you're dealing with a nutjob. Feeling unsafe in your own home sucks.
No one has spoke to the parents. In fact they might not even speak English. I do know a little about them. They have two boys that are between 8-12 that I see a lot outside. in fact the school bus drops them off at my house but almost never see an adult outside or even coming or going.
My neighbor to my right has an email list for people on our street to inform them about news in the neighborhood and is in charge of community watch. He has went over to meet them several time and they will not answer the door.