Social and emotional development during infancy and toddlerhood represents a foundational aspect of human growth, influencing the way children relate to others, regulate their emotions, and develop a sense of self. From birth to around three years of age, children undergo rapid changes in social interaction and emotional expression, shaped by both biological maturation and environmental experiences. Understanding these processes involves examining attachment formation, emotional expression, temperament, socialization, and the emergence of self-concept. Attachment is one of the central processes in early social development. According to Bowlby’s attachment theory, infants are biologically predisposed to form bonds with primary caregivers, typically parents, as a survival mechanism. During the first months of life, infants demonstrate attachment behaviors such as crying, clinging, and smiling, which serve to maintain proximity to caregivers. By six to eight months, infants usually develop a clear preference for familiar caregivers, showing separation anxiety when apart from them. The quality of attachment—secure, insecure-avoidant, insecure-resistant, or disorganized—plays a critical role in shaping emotional regulation and future social relationships. Secure attachment arises when caregivers are consistently responsive, sensitive, and emotionally available, providing a safe base for the infant to explore the environment. Insecure attachments, on the other hand, may result from inconsistent, neglectful, or intrusive caregiving, potentially leading to heightened anxiety, mistrust, or difficulty in forming relationships later in life. Parallel to attachment development, infants and toddlers exhibit a broad spectrum of emotions, gradually gaining the ability to express, interpret, and regulate them. In the earliest months, emotional expressions are largely reflexive and undifferentiated, such as distress, contentment, or interest. As neural and cognitive capacities advance, more complex emotions such as joy, surprise, anger, fear, and disgust emerge. By the end of the first year, infants can show social emotions like embarrassment, pride, or empathy, although these are still nascent and highly dependent on adult modeling and social interaction. Emotional regulation begins as infants learn to cope with discomfort or overstimulation, often relying on caregivers to soothe them. For instance, a caregiver’s calming presence, gentle touch, or verbal reassurance teaches infants that emotions can be managed, laying the groundwork for self-regulation skills that will become increasingly important in toddlerhood. Temperament, which refers to