Developmental psychologists coined the term "theory of mind" to describe how we understand our shifting mental states in daily life. Over the past twenty years researchers have provided rich, provocative data showing that from an early age, children develop a sophisticated and consistent "theory of mind" by attributing their desires, beliefs, and emotions to themselves and to others. Remarkably, infants barely a few months old are able to attend closely to other humans; two-year-olds can articulate the desires and feelings of others and comfort those in distress; and three- and four-year-olds...