This document consists of four research reports and one research note focusing on several aspects of the cognitive and emotional development of young children. The first article explores two theories of the relationship between cognition and emotion, reporting on an investigation of that relationship in a simple learning task involving 60 Japanese infants under 7 months of age. The second article presents results of a longitudinal study of 29 firstborn Japanese infants growing up in urban middle-class nuclear families. Infants followed from birth through 23 months were observed in a standard Ainsworth strange situation; their behaviors in other situations were also analyzed. The third article proposes a conceptual model of the process by which children acquire knowledge through peer interaction in daily situations. The fourth article reports a study, of 4- to 6-year-old Japanese children, designed to test the hypothesis that information about social-cognitive ability and person orientation is required to predict whether or not children will show altruistic behavior in natural situations. Finally, the research note reports a study investigating 1- to 6-year-old Japanese children's ability to discriminate images of themselves from those of other people. (RH)