It feels good to laugh once in a while. Everyone knows that. But laughter as a health-promoting exercise is not as widely practiced, despite the fact that scientists have long known about the potential healing effects of good humor.
I suppose it could be an urban legend that 4 to 6-year-olds laugh 300 times a day. No matter, really. The point is that children laugh way more than adults do. And that ought to tell us something.