See even that doesn't exactly explain the trend. My parents generation had all those risks and more (more deadly power tools and electrics) and the parenting was still absentee at that point. Sure they got into trouble with these things on occasion but a kid learns pretty quick a stove is hot and not to walk into a busy road. In japan they send young kids on errands directly into the modern world where they have all the same risks as they do here, because they understand the value of giving kids a bit of credit.