In a highly endearing interview for The Believer, the late Maurice Sendak spoke of the letters he most liked to receive from children:

When [children] write on their own, they’re ferocious. After Outside Over There, which is my favorite book of mine, a little girl wrote to me from Canada: "I like all of your books, why did you write this book, this is the first book I hate. I hate the babies in this book, why are they naked, I hope you die soon. Cordially…" Her mother added a note: "I wondered if I should even mail this to you—I didn’t want to hurt your feelings." I was so elated. It was so natural and spontaneous. The mother said, "You should know I am pregnant and she has been fiercely opposed to it." Well, she didn’t want competition, and the whole book was about a girl who’s fighting against having to look after her baby sister.

BLVR: You find the unvarnished truth consoling, even if it’s vicious and painful.

MS: If it’s true, then you can’t care about the vicious and the painful. You can only be astonished. Most kids don’t dare tell the truth. Kids are the politest people in the world. A letter like that is wonderful. "I wish you would die." I should have written back, "Honey, I will; just hold your horses."