The Big Book of Pride Flags by Jessica Kingsley with appropriately bold and colorful illustrations by Jem Milton is a fun introduction to the types of flags and the Queer community. Things are not overly in-depth, but it does the job and includes many of the popular flags. Again, the illustrations are fun that accompany things making a nonfiction book (that frankly, could be dull) be loud, proud, and accessible to most ages. There is short, understandable information and the decision guide allows for the parent/educator/healthcare provider to talk with kids and even for the adults to have a better understanding of the subjects. Jem Milton is also the illustrator of The Pronoun Book: She, He, They, and Me! (I have read) and The Gender Book: Girls, Boys, Non-Binary, and Beyond (trying to find a copy).
And speaking of The Gender Book: Girls, Boys, Non-Binary, and Beyond by Cassandra Jules Corrigan, similar information is given about gender and the stories surrounding it. If you are looking for good books to use as introductions to the subjects, this “series” is a must. The combination I recommend reading all three titles (Pronoun Book: She, He, They, and Me! as well) to get the big picture. They are great solo and as a group. I would recommend them for a classroom setting but also for healthcare professionals. 
Corrigan is also the author of My Culture, My Gender, Me, a book I now have on my TBR list dealing with gender expression in other cultures around the world, and Milton has older graphic novels that seem interesting and deal with queer themes. I look forward to finding more!
