How Do I Confront Kids About Kicking Rocks Out of My Flowerbed?

My house happens to be a bus stop. No big deal.  Parents show up, they drop their kids off and most of them wait in their cars until the bus comes while the kids talk and play along my fence line.  Which also isn't a problem... Except that they keep kicking the rocks out of the bed and into the street.

The sidewalk where the children wait runs along my fence line and we have a simple rock bed that follows the length of the street-facing side of the fence. The kids stand in the rock bed and kick the rocks out into the road while they wait for the bus... And they're doing it intentionally.  Every day, when I get home from work, I have to sweep up a bunch of permabark back into the rock bed.  Is it the end of the world? Not really. I doubt the kids are really thinking that the rocks actually belong to someone and cost a fair amount of money. Kids just see rocks and can't help but kick them around. They're simply destructive by nature.

What really butters my biscuit is that most of the parents are waiting in their cars and they can plainly see what's happening. I feel like they should intervene on my behalf and tell their kids to stop kicking my rocks around.

So here's my problem: I really don't want to be the grumpy old man telling kids to "Get of my lawn!"  Is there a polite way to go about this?  Should I throw out a passive aggressive hint by bringing a broom out to the bus stop and sweep up the rocks while the kids are out there?  Maybe I could just tell the kids myself.  As long as I'm nice about it, the parents shouldn't have a problem with it or would they? Should I say something to the parents and pray that I don't wind up with some overprotective mom or dad who's 'little angel' just isn't capable of doing anything wrong? I suppose I could run my front yard sprinklers so they can't stand in front of the fence to begin with. It would certainly solve the the problem without confrontation.

Leave a comment and tell me what you would do?