Friendships in childhood are usually a matter of chance, whereas in adolescence they are most often a matter of choice.

Many older wealthy families have learned to instill a sense of public service in their offspring. But newly affluent middle-classparents have not acquired this skill. We are using our children as symbols of leisure-class standing without building in safeguards against an overweening sense of entitlement--a sense of entitlement that may incline some young people more toward the good life than toward the hard work that, for most of us, makes the good life possible.

Play is not only our creative drive; it's a fundamental mode of learning.

The shift from the perception of the child as innocent to the perception of the child as competent has greatly increased the demands on contemporary children for maturity, for participating in competitive sports, for early academic achievement, and for protecting themselves against adults who might do them harm. While children might be able to cope with any one of those demands taken singly, taken together they often exceed children's adaptive capacity.

If learning to read was as easy as learning to talk, as some writers claim, many more children would learn to read on their own. The fact that they do not, despite their being surrounded by print, suggests that learning to read is not a spontaneous or simple skill.

In leading-edge companies like Google and Apple, workers are given much freedom and opportunity to play. They know that's an important component of creating new and better products. I believe that at whatever level of work, cashier at a supermarket, janitor at an airport, aide in a cubicle, the addition of a playful attitude makes the job better and the work more enjoyable. A cashier or janitor who smiles and is friendly gets a better response than a surly one.

The idea of childhood as a social invention, in retrospect, is hardly credible. In the Bible, in writings of the Greeks and Romans, and in the works of the first great educator of the modern era, Comenius, children were recognized as being both different from adults and different from one another with respect to their stages of development. To be sure, the scientific study of children and the increased length of life in modern times have enhanced our understanding of age differences, but they have always been acknowledged.