There is a lot of grey area here, I guess. I worked as a lifeguard all through high school, and mainly worked, in the summers, at community playground pools.
A lot of the kids would be there 9-5 every single day, because they wanted to be there, they loved it. Some kids were there because the parents sent them there for a few hours. And others were basically on their own. 8 hours with no water, food, or sunscreen, every single day.
If you're looking at 50 kids, yeah, a certain percentage are being neglected. But you can't make a judgment call like that based on a few minutes, because they're a minority.
The concerned woman should have called the mother first, if possible.
Police get called, they have to investigate, that's their job. They could have apologized, seen that there was no neglect, and gone on. Or they could have given a warning.
Police are meant to help communities, in theory.
Unless there's something we're not being told. Maybe the kid had to cross a freeway or something, or is sleeping in an old fridge. Who knows?
But yeah, more likely than not, this is just stupid.