Yep. I used to be park of a park advisory council in Chicago. At one meeting, police were there to field questions about park safety. One of the attendees mentioned their concern for the times they saw "unsupervised 10-year-olds" playing in the neighborhood park. The cop encouraged the person to call 911 when they observed that happening!

In Chicago, it's pretty much illegal to be a kid without an adult present in most places. In the Southern California suburb I live in now, it's better in that respect. Unfortunately, it's not walkable or bikeable outside of the housing development.