I'm not sure specifically without having read the novel. It could be a crucial plot point, a description of a character's thoughts, or perhaps some important dialogue.
I'm not entirely sure specifically what a 'playground novel' is without more context. It could potentially be a self - published or indie - written novel that is in a very early, 'playground' - like stage of development. Maybe it's a story that uses the concept of a playground as a metaphor for life, where different characters interact, grow, and learn lessons much like children do in a playground. It could also be a novel aimed at younger readers, with the playground as a central theme, featuring things like swings, slides, and sandboxes as elements of the story.