As the concept of "mother-tongue shift," which explicitly compares the first languages learned and spoken by parents and their children, suggests, the language repertoires of family members may differ across generations. In this study, the authors consider the possibility that language repertoires differ within the same generation. The results, based on recent Current Population Survey data, first show that the language repertoires of siblings are sometimes different, demonstrating that instances of mother-tongue shift and mother-tongue retention can occur within the same family. The authors also find that the odds of children speaking a non-English language vary according to the sibling position of the child within the household. The eldest child is more likely to speak a minority language than later-born children. Moreover, children's language repertoires are influenced by their siblings' characteristics. (Contains 3 notes, 3 tables, and 1 figure.)