The socio-emotional development of infants and toddlers occurs through intrapersonal and interpersonal relationships. Intrapersonally, infants begin to develop self-awareness, emotions, and gender identity between birth and 3 months of age. Interpersonally, attachment develops as infants smile at and can be comforted by familiar adults by 3-6 months. Between 6-9 months, infants express different emotions, distinguish friends from strangers, and respond to language and gestures. Imitation and self-regulation become more important from 9-12 months as infants mimic actions and show anxiety when separated from caregivers.