Purpose Children with poor language tend to have worse psychosocial outcomes compared to their typically developing peers. The most common explanations for such adversities focus on developmental psychological processes whereby poor language triggers psychosocial difficulties. Here, we investigate the possibility of shared biological effects by considering whether the same genetic variants, which are thought to influence language development, are also predictors of elevated psychosocial difficulties during childhood. Method Using data from the U.K.-based Avon Longitudinal Study of Parents and Children, we created a number of multi-single-nucleotide polymorphism polygenic profile scores, based on language and reading candidate genes (ATP2C2, CMIP, CNTNAP2, DCDC2, FOXP2, and KIAA0319, 1,229 single-nucleotide polymorphisms) in a sample of 5,435 children. Results A polygenic profile score for expressive language (8 years) that was created in a discovery sample (n = 2,718) predicted not only expressive language (8 years) but also peer problems (11 years) in a replication sample (n = 2,717). Conclusions These findings provide a proof of concept for the use of such a polygenic approach in child language research when larger data sets become available. Our indicative findings suggest consideration should be given to concurrent intervention targeting both linguistic and psychosocial development as early language interventions may not stave off later psychosocial difficulties in children.