Thats not much if an issue in Europe. Here the problem is the risk of violence and crime. Particularity in western europe, walking alone at night is risky even as an adult. For kids it would be equally risky during the day.
This concept absolutely exists. First time I witnessed it was in Denmark and Sweden with plenty of stories from locals that were beaten or threatened by local gangs for simply entering their "area" and the police did nothing. Then there are stories I heard from Paris, and Berlin.
However, overall, all areas except maybe small towns and villages pose sufficient risk for children.
Edit: I dont think it’s because of “refugees” as someone else wrote, I think it’s a policing issue.
https://www.tasnimnews.com/en/news/2023/02/16/2854650/sweden...