Mercy Watson Princess in Disguise by Kate DiCamillo

It's Halloween and Mr. and Mrs. Watson's favorite pig is going trick-or-treating! She likes the "treat" part so she's willing to dress as a princess. Of course, in Mercy's mind treats equal buttered toast so when she's offered Halloween candy--well--chaos ensues. Funny, lively with great illustrations. (Mercy Watson Princess in Disguise by Kate DiCamillo, ill. Chris Van Dusen. Candlewick Press, 2007).