BackgroundSiblings are crucial familial-ecological factors in children’s language development. However, it is unclear whether sibling presence is associated with language development among young children with developmental difficulties. The aim of this study was to assess the association between sibling presence and changes in language trajectories of children with developmental delay before early school age. MethodsWe performed a retrospective longitudinal cohort study from December 2008 through February 2016. The medical records of the participants were collected from an official institution designated by Taiwan’s Ministry of Health and Welfare for assessing and identifying young children with developmental difficulties. A total of 174 participants who had developmental difficulties and at least three-waves of evaluations were included in the analysis. Participants’ age ranged from 10 to 90 months. The primary outcomes were receptive and expressive language delays evaluated by board-certified speech-language pathologists. ResultsOf the 174 participants (131 boys; at the first evaluation: mean [standard deviation (SD)] age, 31.74 [10.15] months) enrolled, 64.94% (n=113) had siblings and 35.06% (n=61) did not. At the age of approximately 10 months, the probability of receptive and expressive language delays was lower in participants with siblings than in those without (adjusted odds ratios, 0.19, 0.18; 95% confidence interval [CI], 0.06-0.64, 0.04-0.80; P=0.006, 0.024, respectively). However, at 10–90 months old, this probability of language delay became gradually higher in participants with siblings than in those without, exceeding that of participants without siblings (adjusted odds ratios, 1.04, 1.04; 95% CI, 1.01-1.07, 1.01-1.07; P=0.014, 0.020, respectively)ConclusionsHaving siblings does not necessarily have a positive association on the language development of children with developmental difficulties. Clinicians should consider the association of sibling presence with language development for these children in a broader familial-ecological context.