In Japan they let kids go outside without supervision starting a really young age.
Yeah I live in Japan and my daughter started going on errands ("go get some milk/eggs") alone at age 5. All kids are then expected to walk themselves to elementary school starting from the first week, there is no room for drop-offs from a car.
There's a surprising amount of green for major cities that otherwise look like concrete jungles. There's usually plenty of parks and kids are in general very safe. Maybe this is just my comparison from originally living in the states, but it is super safe for children and the amount of expected unsupervised travel kids do in Japan is astonishing.