DiCamillo writes here in a register entirely her own, catching not the ­whimsical-fabulous note of earlier masters for young readers, nor the jokey-realistic one that has too often taken its place, but instead a mood of sober magic that unfolds into something that can be called, without pejorative, “sentimental,” meaning straightforward and heartfelt. The style may evoke Calvino, but the substance belongs to Christmas.