it does depend on where you live...I grew up in a city of 120,000 and my school was a 5 min walk away and I knew all the kids and parents in the neighbourhood.
We had a program called neighbourhood watch, kids knew that if there was a sign in the door that they could go there for help if they needed to. The parents always looked out for the kids in the area. I used to ride my bike to a friends house and it was 4miles away but I had to call as soon as I got there.
Living in the city however, I wouldn't allow my child to do that..things are getting worse these days and the system isn't helping...overprotecting your kids is a lil over board but being cautious is not. It just depends on what u think is appropriate for that child and their level of perception and intelligence.
