When Children are Free to Play

The player is playing for fun; education is a by-product. If the player were playing for a serious purpose, it would no longer be play and much of the educative power would be lost.

...the child at play is not afraid of failure. The playing child feels free to try things out in a pretend world that would be too risky or impossible to try in the serious world.... Fear and concerns about evaluation tend to freeze the mind and body into rigid frames, suitable for carrying out well-learned habitual activities but not for learning or thinking about anything new.

Play is trivial, but not easy.  Much of the joy of play lies in the challenges.

When children are free to play, they play naturally at the ever-advancing edges of their mental or physical abilities.

Most forms of play involve repetition.

One of the defining characteristics of play is the focus on means rather than ends, and repetitiveness is a corollary of that characteristic. The player produces the same action repeatedly in order to get it right.

But the repetition is not rote. Because the repetition derives from the player's own will, each repetitive act is a creative act. ...the player is deliberately varying the act in some way to fit the game or to experiment with new ways of doing the same thing. A side effect of such repetition is the perfection and consolidation of the newly developing skill.

Free to Learn, Peter Gray, p. 154-5