Just a data point: In Valencia, Spain, in the 80s, children played in the street with no much supervision from parents. Occasionally we would stop the football match to let a car drive by. Forgetting your keys at home was no issue, you could get a glass of milk in ten different places while you wait for other (more attentive) members of your family.

Nowadays there is hardly a place to park your car. Parents don't allow kids to play in the street. And the ones that interact with each other are the ones who lived there in that period. It's very difficult for newcomers to integrate.

What are the reasons for this? My take: cars and lack of stay at home mums. They built the social network at that time. They took care of each other children, the were there to help each other. Nowadays households have both adults working (so nobody even asks for salt to the neighbor, all order a pizza instead).