This essay provides a comprehensive analysis of a three-year-old girl named Ruby, examining her physical, cognitive, social-cultural, emotional, and spiritual development through the lens of prominent developmental theories. The analysis incorporates Garvis's perspective on physical development, Piaget's cognitive development theory, Vygotsky's social-cultural development theory, Erikson's psychosocial development theory, and Bronfenbrenner's bioecological systems theory. The essay highlights Ruby's energetic physical activities, her cognitive engagement with puzzles and symbolic thinking, her social interactions and imitation of her brother, her emotional expressions and parental support, and her spiritual development within her environment. The conclusion emphasizes the importance of understanding child development theories for effective parenting and ensuring healthy stage development through adulthood, noting the theories align with the study done on the child.