I get it for kids younger than 8-10 (depending on the kid), but after that age kids should be able to get out of the house and to school on their own. For the youngest it can be solved with a before school program. The kids just need a place to eat breakfast and chill with their friends before the school day starts.
Letting a child under 18 step outside without being in a car or under direct parent supervision is child abuse in the US and the police will usually be called.
No, there are countless shocking cases of police showing up for things like a child was playing in the front yard unattended while the parent was inside and in some cases the child was taken from the parent due to this “abuse”.
Allowing a 13 year old to walk to a bus stop would be extremely high risk for having police called.
It absolutely happens often enough all across the coutnry to be a serious concern for parents, and you can find plenty of news articles about it with some simple web searches.
I see kids wandering around my neighborhood by themself or in groups all the time, and where I grew up(rural CA), I roamed 5-15 miles away from home regularly on a bike or 4-wheeler.