It can also be expanded by who you expect to be in the circle. If kids are meeting up with friends at a park a mile away, and you know a few of the neighbors in between, that's going to be a quite safe radius.
Yes. My kids have a very small radius because My wife and I are introverts. In nearly 8 years of living in this town we have made 0 close friends. We don't know the people in the next house much less whoever lives by the park. In my defense all the neighbors that I did know recently moved away. But they were all retired. We accidentally moved to a neighborhood with nearly no kids.