The toddler’s face is glowing green from the tablet in her hands, which shows a cartoon boy singing a nursery rhyme and dancing with dinosaurs. The toddler doesn’t know what dinosaurs are or what the ...

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 ...