We often hear about the extraordinary powers of television: the power to amuse and inform the masses, the power to reshape politics, the power to bring together far-flung peoples. These are all significant, but there's another that's even more impressive--the power to keep a four-year-old quiet. All parents know about this miraculous effect, and many take advantage of it without even caring what program is on--Mannix reruns, Cochran and Company, golf--as long as the child sits staring dumbly at the fires of the TV hearth.
Still, no one wants to put the brain of his or her offspring at risk, even...