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"They were best friends, and then suddenly she came home alone." "He's started talking about being left out, or about leaving someone else out." Around ages five and six, the reports that come home from school or daycare start sounding more complicated.
Between ages two and three, friendship means something straightforward: a fun person to play with nearby. By ages five and six, something has shifted. Developmental psychology has described that shift with some precision over the past several decades. Understanding what changes — and why — gives parents a slightly richer vocabulary for listening to their children's social lives.