Groups the phenomena of the psychology atlas whose central finding concerns how a specific cognitive, social or emotional capacity emerges and changes across childhood and adolescence, most often traced to a particular stage or window of development. Belongs here: Object Permanence, the understanding that an unseen object continues to exist; Egocentrism, the difficulty of separating one's own perspective from another person's; Critical Period, the maturational window during which a skill such as vision or language is most readily acquired; Stranger Anxiety, an infant's characteristic distress around unfamiliar people; and the Imaginary Audience and Personal Fable, the twin adolescent-egocentrism constructs identified by David Elkind. A phenomenon whose distortion concerns an adult's ongoing judgment, memory or social behavior rather than the emergence of a developmental capacity itself is filed under decision-making and judgment biases, memory biases and effects, or social biases and group effects instead.