I read this memoir to my son in bits and pieces, between other books. It works well for that because each chapter is a different episode in her life and while she does get older throughout the book, it isn't necessary to remember every detail to keep reading.
I was an adult before I'd even heard of the internment of American citizens of Japanese descent. It was not taught in school in my day (I graduated in 1983). It came as a shock. My son was surprised too, although not as much, as we have read quite a few books about how non-white people have been treated in this country and he's aware that we've treated them poorly, cruelly, and without compassion. Still makes him angry, just not surprised.
He enjoyed Sone's story, especially as much of it is funny, engaging, and takes place in a town we know well, Seattle. The story of the Japanese community picnic, with the careful descriptions of the anticipation, the food, the games, and the behavior was one of his favorite parts. We also enjoyed her visit to Japan to meet her grandparents, and how while she didn't feel she fit in in the US, she didn't feel entirely comfortable in Japan either. And I must say, I loved her outgoing and curious nature. She's a bit of a kick-ass girl, always questioning and pushing the social envelope, which was quite restrictive for women, especially in Japan.
This book has been used in Asian studies courses since in came out in the 1950s and while it's received some criticism for glossing over some of the racism and cruelty, I think that makes it a good fit for younger kids. I think kids as young as 8 would enjoy the first 2/3 of the book, about her childhood. They might be a bit bored by the chapters where Sone is an adult, but those are the chapters that deal with the camp and her move to the midwest (Nisei were allowed to leave the camps before the war was over, as long as they didn't move to the west coast). But at 13, my son did find those chapters interesting.