Arguably, Lily shows herself to be still a child at the end of this novel when her father leaves her, driving away, out of her life. Even though she recognises that she will cease to have any contact with him in the future, she still clings to what she calls "the goodness of imagination" which gives her hope that one day she will actually have contact with T. Ray and he will show love towards her. Note how she phrases this in the final chapter:
Sometimes I imagine a package will come from him at Christmastime, not the same old sweater-socks-pajama routine but something really inspired, like a fourteen-karat-gold charm bracelet, and in his cared he will write, "Love, T. Ray." He will use the word "love," and the world will not stop spinning but go right on in its courses, like the river, like the bees, like everything.
Lily is still a child therefore in the way that she believes in the "goodness of imagination" and how this gives her courage and confidence to believe that she will still be able to heal the ruptured relationship with her father and he will be able to express love towards his daughter. Clearly, this is an impossible dream, as T. Ray is the kind of character who is never going to be able to do this, and Lily hasn't embraced the cold, hard realism of life yet to its full extent.