Infants develop key cognitive and motor skills in their first year. They begin to make voluntary movements by 2 months, develop fine motor skills by 3 months, and gain binocular vision by 3 months. Their language development progresses from babbling at 4-5 months to understanding words and having a 3-word vocabulary by 1 year. Concepts like object permanence and constancy also emerge as infants learn that objects continue to exist even when not seen and remain the same despite appearance changes.