Harold and the Purple Crayon

A 1955 children's book by Crockett Johnson

The protagonist, Harold, is a curious four-year-old boy who, with his purple crayon, has the power to create a world of his own simply by drawing it. Harold wants to go for a walk in the moonlight, but there is no moon, so he draws one.

http://www.youtube.com/watch?v=NzaovPWUb-0