Play is a means by which children develop their physical, intellectual, emotional, social, and moral capacities. It is a means of creating and preserving friendships. It also provides a state of mind that, in adults as well as children, is uniquely suited for high-level reasoning, insightful problem solving, and all sorts of creative endeavors. Oh, did we mention FUN!
Lev S. Vygotsky, “The Role of Play in Development,” in M. Cole, V. John-Steiner, S. Scribner, & E. Souberman (Eds.). Mind in Society: The Development of Higher Psychological Processes, 92-104. (1978, original essay published in 1933).