D..
I read a study one time that stuck with me, mom. It said that children's brains are not developed enough before the age of 10 to be trusted to cross the street by themselves. I was worried enough about my own son that I didn't allow him to take a route home by himself where there was a road that came to a T so that traffic came from behind him, as well as from the left and right. Instead, I had him take a different route, even though he was over 10 years old by then.
Kids' heads are up in the clouds so much so often that it's really best to be safe, rather than sorry. I probably waited until this particular child of mine was in the 6th grade, or even higher.