I think of where I grew up: A very dense city, where streets are narrow, easy to cross, and pre-teens can move around with not just lack of fear, but major convenience. My mother had 4 siblings: All with their families, living in their own apartments. But every apartment was within a 5 minute walk: I could see the other buildings from our building's front door! So if someone needed babysitting, or just had to run random errand, children could be dropped off easily: Cousins almost become brothers when you see them every couple of days anyway.

This was also great for organizing activities with classmates. Not only we got to see each other on the street at random, as we did different errands, but organizing to meet in some bench was trivial. RPGs in the weekend? No problem, as a 15 minute walk catches most of the high school's families.

Now, in the US suburbs, socialization is more about online gaming, because the number of classmates a 14 year old can reach conveniently is pretty low: You could fit an apartment building with 16-20 families in the space that my suburb dedicates to 2. Access to 10 times the people sure makes living next to a friend much more likely! And since drivers aren't needed to get anything done, a lot of things that are commitments in the suburbs just disappear or are easy to move, as another neighbor can take Timmy to the soccer game, as they also have another kid going to the game anyway, and Timmy can walk himself to the neighbor's door with no hassle.

Transit time, and the total dependence of children, are a curse that can be avoided, but we have to do a lot of urban rebuilding for that.