Works of art that express a playful/silly tone might depict characters playing games, behaving absurdly, dancing, or frolicking. Beyond representation, art elements such as light values, high saturation of colors, or lively brushstrokes might contribute to a playful/silly feeling.
An artist might impart a playful/silly tone to a piece due to his or her own light-heartedness, or the artist might choose to evoke this tone as a reflection of the character(s) or scene being portrayed. A playful/silly tone might also be adopted to suit a piece that will be shown in a setting that demands an expression of whimsy.
Featured: Children's Games by Pieter Bruegel the Elder