Anyone who has watched a child play on a playground can see how happy that child is: swinging on the swings and sliding down the big swirly slide. The child is not concerned about whether he is playing with friends he has had for years or friends he just met a minute ago on the monkey bars or in the sandbox.
When children play on a playground, they are simultaneously learning skills that will take them into adulthood. They learn how to compromise by figuring out who gets to go down the slide first. They learn how to negotiate by allotting time limits for the favorite swing. They learn how to make rules by promising to not knock down the sandcastle, and then break rules by kicking it down because they just can’t resist. Most importantly, when kids play, they learn how to get along with other people.