Here's an illustration of how children's freedom has been curtailed over the generations.
If it's not "safe" for children to roam free, then either we have failed at creating a decent society, or we have failed to prepare young people for life; or some combination of those two. If they are not taught how to navigate the world, assess and deal with its risks, then they will arrive at adulthood without those crucial survival skills. And they will have access to far more dangerous things than a sidewalk to bike down or a tree to climb. They'll be driving cars and managing their sexuality, and gods help us all if they don't know how to handle dangers safely before then.
This is so sad. It was already obvious when I was a child in the 70s and is now ridiculous, IMHO.