This chapter explores the integral role that siblings’ multilingual discourse plays across diverse family lives and sites of learning. In discussing key concepts in the field of family studies, young children are viewed as spending as much if not more time with siblings than their parents. This chapter looks at siblings as agentive in shaping the language environment in multilingual families and reflects on research in the area of siblings’ language choices, humour and intimacy as well as sibling rivalry in multilingual discourse. A distinctive feature of sibling relationships is their seriality, and research on the ‘niche’ of each child is looked at in relation to a child’s emerging multilingualism. Siblings’ multilingual discourse is viewed as dynamic and their language practices as in flux as the family grows, moves, or separates. Research on siblings as literacy mediators and studies on their creative multilingualism are examined. This chapter recognises the key role of digital technology in children’s lives and examines siblings’ multilingual discourse in these new digital spaces. New research is shared that investigates how multilingual siblings worked together on an international digital storytelling project.