The Trumpet of the Swan, by E. B. White, illustrated by Fred Marcellino, HarperCollins, 1970.
My first grade son and I were reading this book a few chapters a day for a class project. It is actually a rather lengthy book to read in seven day -- there were about ten pages per chapter -- but my son was enthralled. At the end of each day's reading, he would illustrate his favorite part of what he had read.
I do love this book, but it also makes me a bit sad. It is about sacrifices for love, and, although everything worked out fairly well at the end, I was still sorry for some of the things that had been given up along the way.