my 2 centsno experience on this with my son, but i can share my own personal experiences.
in K-5 grade i lived about a block away from the elementary school, and every morning my mom (she was a stay at home mom until i was about 14 years old) would walk my sister and i to the elementary school, just up to the cross walk.
when i was in 6th grade we moved to an extremely rural area, where we had to walk about a mile or so to the bus stop then ride about an hour to get to school. my mom absolutely would not let me walk alone or even with my sister until i was 15 and i threw such a fit that she finally let me walk on my own. it wasn't that we knew of any sex offenders or abusers in the area... it was just that she knew how many bad people there are out there that are unregistered. she was protective of all of us, and i don't blame her at all; now that i'm a parent, it makes me so sad to see kids who are 5 and 6 years old walking to school by themselves in the morning, then walking home alone at night (i still live in the same rural area)...
also, where i live, it is illegal to let a child under 8 go anywhere unsupervised by a parent or guardian -- if a child is observed to be outside, even out behind an apartment complex playing, without adequate supervision then they can legally get tangled up in CPS (some of the other parents in my apartment complex have dealt with this issue).