It all comes down to the risk you're willing to accept. Back in the 70s when 4-5 kid families were common, population density was much lower and bad things happ

It all comes down to the risk you're willing to accept. Back in the 70s when 4-5 kid families were common, population density was much lower and bad things happening to individual kids wasn't as widely reported? Doing this kind of thing in a nice suburban neighbourhood was fine. Nowadays with far more 1- and 2-child families the risk we're willing to accept is far lower. Population density is higher which directly multiplies the chances of your kid encountering someone who will hurt them. Traffic is busier and drivers are more distracted, increasing the risk of accidents. Distances are greater, there's no "5-minute walk down to the corner shop". All of these factors combine to make the expected cost of letting your kid loose unsupervised much higher and the expected benefit much lower. A 10-year-old would be fine. A 4-year old? Hell no.