It Feels Good to Be Yourself: A Book About Gender Identity written by Theresa Thorn. Hardcover. 

"A picture book that introduces the concept of gender identity to the youngest reader from writer Theresa Thorn and illustrator Noah Grigni. This sweet, straightforward exploration of gender identity will give children a fuller understanding of themselves and others. With child-friendly language and vibrant art, It Feels Good to Be Yourself provides young readers and parents alike with the vocabulary to discuss this important topic with sensitivity."