What can we do about destructive neighborhood kids?

My boyfriend is an avid collector of classic cars which he keeps in his driveway. About 3 months ago a new family began renting the house across the street. Their kids are little monsters. They run around in his driveway, jump on top of his classic cars like they're jungle gyms, kick the cars, and spit on them. Two of his cars are already showing body damage from the daily beatings they take. We have asked the kids multiple times to stay out of the drive way and away from the cars but they won't listen. And we have actually witnessed the parents just standing by and watching as their kids throw stuff and climb on the vehicles. We would talk to the parents however the father acts like he doesn't speak english and the mother is almost always away at work. We don't want bad blood but we are absolutely fed up with the kids disrespecting our property. My honey has been incredibly kind to these kids, even giving them video games and they continue to disrespect our wishes. What can we do to get these heathens to stop?!