One of my favorite books to use in kindergarten or first grade to teach about diversity and prejudice is A Pig Is Moving In by C. Fries. When Henrietta Hen, Nick Hare, and Doctor Fox learn that a pig is moving into their building, they are appalled. Everyone knows that pigs are dirty and messy, and this pig seems to be no exception. While neither Henrietta, Nick, nor Dr. Fox has had a chance to meet the pig in person, careful observation has confirmed their worst fears.
I begin by asking these pre-reading questions:

Can you look at someone and know what kind of person they are?

Have you every met someone who didn’t like you before they got to know you?

Why did the neighbors pre-judge Theodore?

This book facilitates a discussion of all types of differences.  For other ideas to teach children to be kind to others check out State of NJ Caring Makes a Difference