I grew up in a relatively large town (~300k at the time, regional capital), on a block that mostly consisted of densely packed 5-story and 8-story apartment buildings.

We all played all over the neighborhood together. There were playgrounds between the buildings, but we didn't really stick to them once we were old enough to go to school. When I was 10, I was riding the bike all over the place, within about 5km radius from home, and so were all the other kids.

I didn't personally know anyone who had a serious accident, traffic or otherwise. The worst I remember is one kid falling off the garage roof and breaking an arm, and another kid riding the bike into an uncovered manhole and falling down there. As far as the rumor mill went, the most extreme that I can recall was a story of a kid in the area who lost an eye in an incident involving live ammo being thrown into fire.