I have direct experience with this topic. My nephew was allowed to walk 2 blocks home when he was in 2nd grade.
One night around 7 I got a call saying he hadn't come home. It was a traumatic experience. He and a friend decided to explore a drainage ditch halfway home. At around 9pm the police brought them home. They followed the ditch until it ended at a major street, after dark, and someone called the police.
This topic deals with 2 factors mainly. You can't fully rely on children, and you can't trust all adults. I will always end up on the safer side of this topic. My sister was at home, 2 blocks away and thanks directly to God, it didn't end tragically.