From tracking a conversation mid-topic to revising a plan as new information arrives, the ability to update mental representations is central to o how we navigate a dynamic world. In children, this ability is a foundational component to their cognitive development, yet its developmental mechanism remains poorly understood. This thesis addresses this question by examining the developmental trajectory and its relationship with working memory capacity across two studies. Study 1 presents a meta-analysis (99 studies, N = 35,858) of working memory updating development from early childhood through adolescence, identifying systematic patterns of growth and examining how task characteristics shape developmental sensitivity. Study 2 (N = 124) develops and validates a novel paradigm for assessing working memory updating in young children. Using CFA and bifactor modeling, the study clarifies relations between working memory capacity and updating. Together, findings advance understanding the development of working memory updating and provide validated, theoretically grounded tools for measurements in early childhood.