Children develop artistically just like they do in other areas of their life, like walking and talking, it comes in stages. One of the leading theorists on the subject is Dr. Viktor Lowenfeld, who published "Creative and Mental Growth" in 1947, breaks down the artistic stages in terms of mark-making.
The website The Virtual Instructor has a wonderful blog entry detailing Lowenfeld's work with the wonderful imagery below: http://thevirtualinstructor.com/blog/the-stages-of-artistic-development
The website The Virtual Instructor has a wonderful blog entry detailing Lowenfeld's work with the wonderful imagery below: http://thevirtualinstructor.com/blog/the-stages-of-artistic-development