One

One simple book about colors.
One simple book about numbers.
One simple book about overcoming adversity (or bullying).
One simple book about working together.

One by Kathryn Otoshi.

Don't be deceived by the simple look of this book. It touches many concepts and can be used in many different ways.  It can be shared with much older children as well as the preschool crowd. The modest watercolor illustrations keep the focus on the colors and numbers and add emotional impact.
Adults may enjoy this book even more than the children.

Art Extension Idea:
Shaving Cream Colors
Materials:
Shaving cream, paint in primary colors (red, blue, yellow), plastic sandwich bags that close tightly, spoon
Procedure:
Give each child a plastic bag and have them open it (assist if they need help). Spray a "handful" of shaving cream into the bag. Add a squirt or spoonful of one color of paint.  Close the bag tightly.  Encourage each child to squeeze and manipulate the bag to mix the color into the shaving cream.
Repeat the process with a second bag but this time add two primary colors. Watch and listen to the children as they observe what happens inside the bag as the two colors mix.
Non messy and it doesn't require drying time!