Final answer:
The two major theories of infants' social development are attachment theory and psychosocial theory, each proposed by John Bowlby and Erik Erikson, respectively.
Step-by-step explanation:
Two major theories of infants' social development are attachment theory and psychosocial theory.
Attachment theory was proposed by John Bowlby and focuses on the emotional bond between infants and their primary caregiver. It suggests that infants develop an internal working model of attachment based on their early experiences, which influences their future relationships and social development.
Psychosocial theory, proposed by Erik Erikson, emphasizes the interaction between an individual's biological maturation and the social environment. It posits that individuals go through eight stages of psychosocial development, with each stage presenting a unique social challenge that must be resolved. Successful resolution of these challenges contributes to healthy social development.