Trust vs. mistrust is the first stage of Erik Erikson's psychosocial development theory, occurring from birth to approximately 18 months. During this period, infants learn to develop trust when caregivers provide reliable care and affection. If a child's needs are consistently met, they feel secure and develop trust; however, inconsistent or neglectful caregiving can lead to feelings of mistrust and insecurity in the child, impacting their future relationships and emotional well-being.