There is a focus in the article in playing outside which is good and fine.

But another important aspect missing today is age mixing. This is crucial because it is an informal mentoring process, in effect. 4 year olds learn best from being around 6 year olds who learn best from 8 year olds, etc. up the chain. There is also reflection from being a mentor to the younger ones. All of this is absent increasingly today.

It is not just lack of recess or whatever, but a lack of neighborhood, of community. The young ones learn how to share, how to regulate emotions, etc., in part by witnessing the older ones being that way.