Sibship size, sibling cognitive sensitivity, and children's receptive vocabulary.

OBJECTIVES: The aim of the current study was to examine the relationship between sibship size and children's vocabulary as a function of quality of sibling interactions. It was hypothesized that coming from a larger sibship (ie, 3+ children) would be related to lower receptive vocabulary in children. However, we expected this association to be moderated by the level of cognitive sensitivity shown by children's next-in-age older siblings.
METHODS: Data on 385 children (mean age = 3.15 years) and their next-in-age older siblings (mean age = 5.57 years) were collected and included demographic questionnaires, direct testing of children's receptive vocabulary, and videos of mother-child and sibling interactions. Sibling dyads were taped engaging in a cooperative building task and tapes were coded for the amount of cognitive sensitivity the older sibling exhibited toward the younger sibling.
RESULTS: Hierarchical regression analyses were conducted and showed an interaction between sibship size and sibling cognitive sensitivity in the prediction of children's receptive vocabulary; children exposed to large sibships whose next-in-age older sibling exhibited higher levels of cognitive sensitivity were less likely to show low vocabulary skills when compared with those children exposed to large sibships whose siblings showed lower levels of cognitive sensitivity.
CONCLUSIONS: Children who show sensitivity to the cognitive needs of their younger siblings provide a rich environment for language development. The negative impact of large sibships on language development is moderated by the presence of an older sibling who shows high cognitive sensitivity.