The picture should be large without small details, images must be recognizable, kind and interesting, for kids contour lines should be thick, it hides some errors made by child, the outlines of the pictures should be smooth, without corners, difficult bends.
Did you know that Carl Jung ordered some sort of coloring to his patients? The psychoanalyst asked them to fill paint into the cell, in order to access to the subconscious and customer self-awareness. Today this method is considered obsolete, but the coloring shows many patients as an alternative to meditation, relaxation and soothing agent practice. Coloring helps a person to focus on the picture and the small details, throwing a few hours all of your obsessive thoughts and anxieties.