...We have approached a neighbor (It's just a team "thing" I was told, point blank.) and the parents with the kids in the car that we caught in the act ("They're just having fun" the mom sneered.) It has recently come up on Nextdoor, with the responders about 50/50. The common retort is "lighten up". We have also spoken to the police, who have no interest in stepping in....
What you are describing here is trespass. Trespass to land
by itself is not a crime in California (or most places), although it can be a crime if combined with various other circumstances. However, unless one of those special cases apply, the appropriate remedy for trespass is a civil suit. Furthermore, even in the special cases where trespass is a crime, it is only a misdemeanor. Cal Penal Code § 602. In California, the police generally have no power to arrest a person for a misdemeanor unless (1) the officer has a warrant authorising the arrest, or (2) the offense was committed in the officer's presence. Cal Penal Code § 836. There was likely nothing the police could do about your complaint.
I was reminded of this thread after
a similar post I made in another thread. In general, the police do not exist to adjudicate legal claims. That is the function of the courts, especially on complicated topics like property law. Most police officers do not have the legal training to evaluate the veracity of property law claims.