There are not many children's books that are published without words. This is in part due to the emphasis on learning how to read and write in the first couple years of school. This is unfortunate, since wordless books are excellent tools for helping children develop the basics of language while introducing them to underlying story structures and stretching their imaginations.

The book a boy, a dog, a frog and a friend by Mercer Mayer is an excellent example. This short but powerful book says it all in illustrations with the characters' actions, body language and expressions. There is just enough structure to the story, so that children do not get frustrated by having too much latitude in plot, but just enough flexibility that allows them to be somewhat creative in their descriptions of the illustrations. They can answer questions, such as "How does he feel?" (emotions) or "Why do you think he did that?" (reasons for actions)...

It helps them gain confidence as they begin to express themselves through their own words. It also lets them know that most stories have a beginning, middle and end and read in a left-to-right pattern. In addition, they learn to see and explain details and draw conclusions from them and to detect mood and feelings from looking at other clues rather than words. They gain all this and more from just looking at several wordless pages that tell a wonderful story.
References

Mayer, Mercer. A boy, a dog, a frog and a friend. New York, Penguin, 1978.