I think a lot of kids could actually care for themselves at age 9. I think the problems might arise if there was some sort of unusual problem that the kids didn’t know how to handle: a prowler, a medical emergency, etc. Also, I wonder how it affected them emotionally to know their parents had shrugged them off for so long — whether they felt empowered, or abandoned. I guess that would depend on the kid and the relationship with the parents.
We were early gentrifiers in a run down urban area. One Saturday, I was enjoying late morning snoozing when my 10 year old came in and said he needed to talk with me. He had been walking near a small construction job up the road when 3 kids approached him and demanded money. He said they were about the size/age of his 13 year old brother. They chased him and he grabbed a 2 foot length of rebar and ran to the top of a sand pile. He kicked one in the stomach and slashed the ring leader across the face with the rebar. His comment, “did you know that fat is yellow?” I do now. Then they ran off. His thought for the day, “They must have thought I was one of those wimpy white kids from the suburbs.” Years later he told me he was known at his junior high as “the white kid who knows how to fight.” He is my mellow son, his older brother is in Special Forces.