Fifty-five years ago, preschoolers were captivated by the TV performance of a fuzzy blue monster, two striped shirt-wearing best friends and a big yellow bird. Today, in the now-crowded field of ...

Two small children jump into a bubble bath with expressions of dazed, perpetual pleasure. The taller one has hair like molded chocolate, the other’s is like a yellow ice-cream swirl. Everything—the ...