Objective This study examined long‐term developmental changes in mother‐rated lower‐order facets of children's Big Five dimensions. Method Two independent community samples covering early childhood (2–4.5 years; N = 365, 39% girls) and middle childhood to the end of middle adolescence (6–17 years; N = 579, 50% girls) were used. All children had the Belgian nationality. Developmental changes were examined using cohort‐sequential latent growth modeling on the 18 facets of the Hierarchical Personality Inventory for Children. Results In early childhood, changes were mostly similar across child gender. Between 2 and 4.5 years, several facets showed mean‐level stability; others changed in the direction of less Extraversion and Emotional Stability, and more Benevolence and Imagination. The lower‐order facets of Conscientiousness showed opposite changes. Gender differences became more apparent from middle childhood onward for facets of all dimensions except Imagination, for which no gender differences were found. Between 6 and 17 years, same‐dimension facets showed different shapes of growth. Facets that changed linearly changed mostly in the direction of less Extraversion, Benevolence, Conscientiousness, Emotional Stability, and Imagination. Changes in facets for which nonlinear growth was found generally moved in direction or magnitude during developmental transitions. Conclusion This study provides comprehensive, fine‐grained knowledge about personality development during the first two decades of life.