I think understanding social norms and being respectful of strangers is essential, of course. But I personally don’t think that “playing with” a large group of strangers is a necessary skill, or has any parallel in adulthood, that’s the point I was trying to make. This is just my opinion, of course. I like going to parks, letting them climb trees, having playdates, and going to classes; in those environments, they learn sharing, playing, courtesy, all the things they need to learn but it doesn’t require them to play in an unstructured environment with a group of strangers. And of course school playgrounds are great because they know the other kids, and there’s an agreed upon set of rules and adults who are all working together to enforce them. I like that semi-structured environment much better, I think much more constructive learning takes place.