The Trumpeter of Krakow might be a little long for a first foray into chapter books. But then again, my mother read me all of Laura Ingalls Wilder's Little House books when I was pretty young, and they're pretty long, so maybe length doesn't matter so much? At least for a reading-aloud book.

When I first learned to read, I loved Cynthia Rylant's Mr. Putter and Tabby series. They're technically chapter books, but the chapters are very short, so they weren't frustrating at all to my first-grade self.