Enchanted Island of Yew, The by BAUM, L. Frank

A fairy has become bored with her life, and convinces some young girls to transform her into a human boy so she can go on adventures. The adventures come fast and furious, as the newly-named Prince Marvel explores the surrounding kingdoms. A masochistic squire accompanies Marvel, helping him with assorted kings, knights, dragons, and other medieval menaces along the way. (Summary by Ted Delorme)