I bought this book in a discount bin (along with William's Doll, another inexpensive paperback classic!) many years ago when my older kids (now 13 and 14) were toddlers.
I brought it out recently when my father died and it sat all week in our shiva house, where it evoked a whole range of reactions from all the adults my 3-year-old daughter asked to read it to her (over and over and over, which should tell you something).
While many adults reading the book were taken aback by the format of words appearing on pages with no pictures (and vice versa), kids have always seemed to understand it intrinsically: the format forces you to hear the words, pause, see the picture, then pause again before the next words.
This format uniquely allows kids breathing room to think their own thoughts about the pictures and the story.
Other adults were appalled that the children were dealing with death all alone, and that the book actually used the word "dead" without euphemism. Again, that's a-okay in my book: the right words are the only words I try to use with my kids, even if those words are not always lovely. There'll be time enough later on to learn the thousand euphemisms for death.
A few practical folks just pointed out that it's not advisable for anyone to handle dead wildlife. Of course not. I make a point of telling my kids that if they find a dead bird (especially in this era of West Nile) that they're to come show me.
In any event: the book. The simple, childish illustrations by Remy Charlip are timeless and unforgettable and complement the simplicity of the storyline perfectly.
The last page of the book adds so much simply by mentioning that the children do eventually forget about the dead bird. In the final picture, they're playing ball in a nearby field. It's a beautiful day: life goes on.
Death is part of life, but it's not what life is all about. Life, especially for kids, is about the ballgames, and the grief / mourning process is how we get ourselves back to that normal.
Unlike other books for kids about death, it doesn't deal at all with the specifics of dying OR losing someone you love. It simply begins when the bird is dead. Those are important themes, but for younger kids, I have found it so helpful to break it down: the conversation about death does not HAVE to be the conversation about dying, if that makes any sense.
Piece by piece, kids eventually make sense of the world around them. Books like this one really help.