3. Can I Play Too?, by Mo Willems
As an accomplished cartoonist, Willems has a way with words and pictures. This book is a part of the famous Piggie and Gerald series, and shows how two best friends, a pig and an elephant, welcome a new friend who is different from them into their group so they can all play together, even though they have very different abilities.

4. The Sandwich Swap, by Queen Rania of Jordan Al Abdulla
This book about two best friends with very different lunches teaches kids that friendship is stronger than difference, and that tolerance and acceptance are key ingredients to any loving relationship between best friends.