Once Upon a River centers upon the discovery and miracle of the unnamed child pulled from the river by Henry Daunt. Her appearance is left vague as many characters do not agree on what she looks like. Her eyes are described as blue or grey or green, depending on who is discussing her, and her hair is “the same color dry as wet” (45), though what that color is goes unexplained. She is small and she does not speak to any adults in the novel. The vagueness of her physical appearance adds to the mystery, for without defining characteristics she remains difficult to place.

The Child represents different things to the different people who claim her. To Lily, she is a link to the past and a sin to absolve. The Armstrongs see her as an extension of their eldest son and wish to give her the protected upbringing that children deserve. The Vaughans believe her to be their lost daughter and wish to raise her as their own; even after the revelation that The Child is not Amelia, they still accept her as their daughter. The regulars at the Swan see her as a story in progress, something mystical that becomes more complicated with each telling.