Preschool Socio-cognitive and Language Development in the Context of the Sibling Environment

Children’s socio-cognitive and language development occurs in the context of social interactions, including those involving siblings. Using data from a longitudinal birth cohort study, the current thesis investigated the contributions of structural and process-based features of sibships to children’s socio-cognitive and language development. Using a cross-sectional design, Study One (N = 385) explored sibship size (i.e., number of children in the home) and older sibling cognitive sensitivity as contributors to younger siblings’ receptive vocabulary (M age = 3.15 years, SD = .27). Results indicated that children from large sibships (i.e., 3+ children) had lower receptive vocabulary scores in the absence of a sensitive older sibling. Using a longitudinal design, Study Two (N = 385) investigated these same variables in predicting younger siblings’ theory of mind development approximately a year and a half later (M age = 4.77 years, SD = .26). A similar pattern emerged wherein children from larger sibships had lower theory of mind scores in the absence of a sensitive older sibling, after controlling for earlier theory of mind. Using a within-family design, Study Three (N = 288) explored birth order and sibling prosocial behavior as predictors of younger siblings and older siblings cooperative abilities when they were the same age (M age = 3.33 years, SD = .39). Laterborn children demonstrated enhanced cooperative abilities, particularly if their siblings showed higher levels of prosocial behaviour. The current findings demonstrate the utility of investigating the ways in which sibling factors combine to influence children’s social cognition and language. The relationship of receptive vocabulary, theory of mind and cooperation to one another, as well as the ways in which they shape and are shaped by their social environments are discussed. Implications of the findings for intervention studies designed to promote sibling responsivity are also discussed.Ph.D