Two is a Team is a very early picture book that details a friendship--and conflict--between two little boys as they work on a project together. One is black, one white. Published in 1945 by Lorraine and Jerrold Beim, it predates a celebrated May Justus book about segregation, New Boy in School. It may seem this is an old subject, already dealt with, but it is always useful to talk about teamwork with kids. I got this book from my local library, and it is also available from used-book sellers.