Because that's not what the police report was about?
The police don't get summoned because kids are causing problems. They are getting summoned simply because there is no adult visible.
The OP isn't making some outlandish claim that requires massive amounts of evidence for us to accept. There are thousands of stories attesting to this kind of thing.
I see kids out side on their own all the time, even in suburban California like some other comment suggested is an issue
"What else are you supposed to do?" Focus on something else. The cops are for enforcing the law, not for making you feel better.
So what are you supposed to do?
The US is truly and utterly deranged. Kids should make their own experiences throughout their neighbourhood. And neighbours should scold them if they behave like shit. This is literally how it has been for most of humanity.
For instance buying apartment next to basketball playground and then complaining about kids playing there basketball and making noise is not police business but idiots call police on kids having fun, apparently they should be better staring at phones at home, so old people can then complain kids nowadays don't spend enough time outdoors.
Then now add the scenario where it's probably socially unacceptable to interact with other people's kids