The phrase latchkey kid comes from the boomer generation. For kids with working parents, they were tasked with getting home and staying safe even when their parents weren't there. They'd come inside and lock the door with a latchkey. Sometimes, a sibling would keep them company, but not always...
Childproofing a home is common practice today, but once upon a time, this was not the case at all. Babies would roam freely at the same height as electric outlets, cabinets, drawers, and hidden cleaning products. It was a parent's job to keep an eye out...constantly. Yikes!