Depending on where you live, police will be called.

Then pass Karen's Law and start fining the people making those calls if made without good reason to believe of imminent or reasonable danger to the child. It not only screws up society, but is a complete waste of resources.

In the US at least, we've gotten to the point that kids under 10 are rarely trusted to be alone and parents risk neglect charges by leaving them. Even the 10-13 range could be a risk. The problem is if someone calls the cops or social services, enough of those departments will take it seriously that as a parent, you really don't want to risk it.

It's a problem, because it's raised the bar for expected supervision effort, likely far beyond what is really needed.