Pretend Soup and Other Real Recipes by Mollie Katzen is a terrific kids' cookbook. Katzen is the author of the popular Moosewood cookbooks, but I think her kids' cookbooks are even better!
Each recipe is written out in a 2-page spread for the grownup helpers: the recipe typed up, advance preparation notes, tips for working with the preschool crowd, clean up tips, and so forth. Then, a 2-page spread follows for the preschooler: 6 pictures per page plus minimal text show which ingredients to add when, whether to stir or not, how long to cook, etc. The directions are clear enough that my 4-year-old is able to follow the recipe quite easily; to date she's successfully made Surprise Oatmeal, Popovers, and Noodle Soup.
Recipes go beyond simple graham cracker snacks and include "Surprise Oatmeal," "Pretend Soup," "Noodle Soup," "Popovers," "Quesadillas," "French Toast," and many more.
Here's what my daughter (almost 5) has to say in answer to the question, "What do you like about this book?"
"It has many ingredients to make. I like it because you can make oatmeal, muffins, and popovers. You can help your Mommy."