Hi!
I had a similar problem with one of my neighbors. Their pine tree has always shed its needles and pine cones all over my car-port and driveway, since 1995. I never really thought it was totally their fault, because Hey, it's a tree, and always cleaned them up myself. Then late one fall my fruitless mulberry trees (I have four, two up front and two in the back) had shed some of its leaves into their swimming pool, probably due to the wind. She actually fished them all out and, get this, threw them over an 8 foot fence, back into my yard! I probably could have handled that just find, until she informed me that I should make sure that doesn't happen anymore!!! So I cleaned up the mess from their pine tree, cones and all and threw them over her fence, they just happened to land in the pool. I just made the comment that the wind must have been very bad the night before, she couldn't say much, because it was her tree. Before that, their kids would terrorize my dogs. Climb up an 8 foot fence ans tease them! This is what makes most dogs aggressive with kids. When she did nothing about it, I caught them at it and told them it had better stop!! They had moved up to throwing rocks at them. Then I told the parents that I had it on video, and it is considered animal cruelty, and I would report them if it ever happened again!! I haven't caught them at it again. I would hope you have better luck with kindness than I did. But you may have to result to turning the tables on them....GOOD LUCK!!