"Leave lots of room for illustrations. I mean LOTS of room. This is the best way to cut down your number of words, and the hardest thing for most writers to do (unless you're also an illustrator, in which case you've got an advantage here). First, study books with short texts and see how much of the story is contained within the pictures. Then write your first draft, forgetting about word count. As you revise, think about what each illustration might look like. It helps to create a 32-page "dummy" book and put your text on 26-28 pages (leave the other pages blank for title page, copyright, end pages, etc.). * HERE IS THE EXCITING PART! Then write a description of each illustration, or sketch one out (don't worry, no one will see this but you). Now, what do you say in the text that's also depicted in the pictures? Take it out of the text. It doesn't need to be stated twice. Kids are looking at the illustrations while an adult is reading the words, so they'll get that information."
And let me tell you, IT WORKS! Kaboom! Useless words are out! Try it and let me know how it works for you!