A preposterous mustasche is the plot device used in this humorous re-imagining of the baby/toddler years.
The eponymous baby in Mustache Baby is Billy, whose apparent transformation from “good” to “bad” (a metaphor for the angelic baby stage vs. the terrible-twos stage) is reflected in how his mustache changes as he grows — at least, that’s the tale spun by the punny text. The accompanying illustrations, however, tell a whole other story that rings chaotically truer to life, and this clever juxtaposition of fantasy and reality is what makes the book brilliant.
But even if you don’t read between the lines, as kids are unlikely to, the adorable illustrations are utterly irresistible.