Final answer:
The nurse practitioner would be most concerned with the child's emotional development as it is crucially influenced by early attachment and the mother's mental health could significantly affect their ability to form healthy emotional connections.
Step-by-step explanation:
In the scenario where the mother of a 3-year-old child has been treated for depression for over 5 years, a nurse practitioner would likely be most concerned with the child's emotional development. This concern arises from the critical nature of attachment in infancy and the nurturing environment's role in a child's psychosocial development. Developmental psychologists emphasize that early attachment and emotional connections significantly influence a child's capacity to form relationships, self-regulate emotions, and engage in social interactions as they grow.
Therefore, among the options provided, which are cognitive development, social development, physical development, and emotional development, the nurse practitioner would be most attentive to the child's emotional development, given its foundational influence and potential impact stemming from the mother's long-term mental health condition.