Calling Child Protection for such trifles should be criminal.
I completely relate.
I had a stranger come knock on my door to warn me that my five-year-old daughter was playing outside by herself.
On my front lawn.
When I told him, non-chalantly, that I knew, he looked at me like: aren't you worried?
It should be assumed that kids playing by themselves within a reasonable distance from their houses are not in grave danger.
At what age? How far? It's a judgement call. I think they're fine if they're within the block, are verbal, self-aware and can express their wants and needs. As the mother of autistic children, I have given this some thought.
Kids should be able to play outside, even alone. It's good for them.
H/T: Lenore Skenazy at Reason.