Mudkin by Stephen Gammell (Carolrhoda, April 2011) is an clever book about an imaginary friend, in this case, one that comes from playing in the mud. A little girl discovers a mud creature called Mudkin who invites her to his castle where she will be queen. Although there is little text (Mudkin does not speak English but actually in muddy smudges), the story celebrates imagination.
I loved the muddy illustrations and loved the overall effect of the story. My four-year-old son liked it, and I suspect older children may grasp the imaginative aspects of the story more readily than he did. As an adult, I loved it. My son needed some prompting to understand it.