Kira-Kira by Cynthia Kadohata. It won a Newberry medal for children's literature, which it completely deserved.
I cried my eyes out, I cried like a little kid with a lost puppy, I cried so hard my cheeks ache. If you can read this and not cry, seek help. I had to make a special trip out to see my best friend's daughter (we are very close) just to hug her. She seemed surprised, but I gave her the book. I'm expecting her to call me in tears for a hug very soon...
10/10. Utterly flawless- perfect for humans of any age, culture, ethnicity, or religion.