Background: Children with developmental language disorder (DLD) are at higher risk of poorer mental health compared with children without DLD. There are, however, considerable individual differences that need to be interpreted, including the identification of protective factors. Aims: Pathways from the early language and communication environment (ELCE, 1-2 years) to internalizing (peer and emotional problems) and externalizing (conduct problems and hyperactivity) problems in middle childhood (11 years) were mapped using structural equation modelling. Specifically, the role of indirect pathways via social skills (friendships, play and prosociality) in childhood (7-9 years) was investigated. Methods & Procedures: Secondary analysis of existing data from the Avon Longitudinal Study of Parents and Children (ALSPAC) was undertaken. The study sample consisted of 6531 children (394 with DLD). Outcomes & Results: The pathways from the ELCE to internalizing and externalizing problems were similar for children with and without DLD. For both groups, a positive ELCE was associated with more competent social play and higher levels of prosociality in childhood, which in turn were associated with fewer externalizing problems in middle childhood. Furthermore, better friendships and higher levels of prosociality in childhood were both associated with fewer internalizing problems in middle childhood. Conclusions & Implications: A child's ELCE is potentially important not only for the development of language but also for social development. Furthermore, in the absence of adequate language ability, play and prosocial behaviours may allow children with DLD to deploy, practise and learn key social skills, thus protecting against externalizing problems. We suggest that consideration be given to play- and prosociality-based educational and therapeutic services for children with DLD.