I live in Illinois and I knew there was a bit vagueness in the law for kids left alone, but I wouldn’t chance it.
When I was younger, it wasn’t until high school when I was left alone in charge of my brother who is 6 years younger than me. And we still had all out fights - to the point where he pulled a steak knife on me. But it all ended well and we’re good friends now. 
great band name! 
Mine are currently 11 and 12.
My mother has watched them the past two summers. I’ll leave mine alone together for a day - but not longer than a day - too much junk food, bad tv and “running feral” - not to mention the sibling battles.
The summer before that they had “day camp” at the community center. Before that, when they were little (like until the oldest was in third grade) they did summers back at their old daycare.
Next year, I’m not sure what we will do. They are getting a little old for Grandma, but a little young yet to leave alone.