Multi-child households have a built-in play advantage, and specific challenges. Here is the research on sibling play and how to make the most of it.
Siblings are, developmentally speaking, one of the best things that can happen to a child's social and emotional development. Research by Judy Dunn at the Institute of Psychiatry shows that children with siblings show earlier development of theory of mind (the capacity to understand that others have different thoughts and feelings), better emotional vocabulary, and stronger conflict resolution skills, all driven by the daily practice of navigating a close relationship with someone their own age.
Key citation
Dunn, J. (1988). The Beginnings of Social Understanding. Harvard University Press · Perner, J. et al. (1994). Theory of mind is contagious. Child Development
Sibling conflict is uncomfortable, and developmentally productive. Children who learn to negotiate ownership of a wooden toy, take turns, and repair ruptures with siblings are building exactly the social problem-solving skills that predict positive peer relationships in school. The parent's role is not to resolve every conflict but to scaffold its resolution: "What could you each do with the fox?" not "Here's a different toy for you."
Toys designed for shared play →Britain's oldest toy maker. Every toy open-ended, wooden, and built for exactly the kind of play the research recommends.