ETA relevant links: https://youtube.com/@NotJustBikes https://letgrow.org/
ETA again: I glibly mentioned "being killed by a driver" but of course navigating the typical US built environment if you're under 16 or otherwise unable to drive is a miserable experience in a number of ways even if you survive it. Highways make pedestrian paths unnecessarily roundabout. Parking lots make everything further from everything else. Crossing major roads requires getting drivers to notice and stop for you (harder when you're short!), or waiting through interminable signal cycles, etc.
This is true on the Internet, but not true in any real life place I've lived in the US.