This study investigates the father's contribution to child development in the context of a triadic family constellation, integrating data that parallel previous investigations of fathers: differences in children's behavior to mother and father, differences in mothers' and fathers' behavior to the child, and correlations between parental and child variables. The study treats the family triad as a system that is dynamic, examining the interactive behavior of mother, father, and child as they change over time. Data are drawn from a 1972-1973 longitudinal study of 14 children from 1 to 2 1/2 years of age. Children in the study were randomly selected from hospital birth records. All families were white, but a range of socioeconomic levels from working class to professional class was represented. All mothers were nonworking and were their children's primary caregivers. Data was gathered from: unstructured observations of child and family at home, semi-structured situations, questionnaires (daily records kept by the mother) as to the child's activities as well as questionnaires investigating parental attitudes towards the child; and assessments of the child's intellectual competence. A number of results were found and are discussed in some detail, including differences in amounts of child's interaction with mother and father, parent-initiated behavior, mother's and father's social-physical play with the child, mother's and father's verbal interaction, and effects of mother's and father's behavior on the child's development. (Author/MS)