We know that Inside Out and Back Again is for young readers for a few reasons. First—and importantly—the language is really accessible. No big fancy words, no super complicated sentences, no dictionary needed. Also, Hà is the main character and she is ten years old throughout the whole book, which means she really speaks to younger readers. Of course, none of this means that older people can't get totally swept away in Hà's story. We sure did, and we haven't been ten for, well, let's just say it's been a little while.
Hà's story takes place during some major historical events, and although it isn't a non-fiction book, it is based on real events from the author's life. Since a bunch of the story is made up, it's firmly rooted in the fiction genre, but since so many other events really did happen—especially the Vietnam War—it's not just any old fiction, it's historical fiction. For example, at one point a pilot brings the following news to everyone on the navy ship:
At noon today the Communists crashed their tanks through the gates of the presidential palace […]. (1.34.12)
This event actually happened, signaling the end of the war in the real world just as it does in the book. When stuff like that happens, Shmoopers, chances are decent we're in historical fiction territory.