|informal something that is easy to do|
|a children's mummer's parade, as on the Fourth of July, with prizes for the best costumes.|
|an arrangement of five objects, as trees, in a square or rectangle, one at each corner and one in the middle.|
Something easily done, a trivial matter. For example, Finding the answer was child's play for Robert, or The fight we had was child's play compared to the one I had with my mother! Originating in the early 1300s as child's game, the idiom was already used in its present form by Chaucer in The Merchant's Tale: "It is no child's play to take a wife."