"Why aren't children in the early years doing an abundance of writing?"

Back in the 90’s when I was a teacher in the public school system I was trained in the New Jersey Writing Project. We learned to teach children the writing process through something called Writer’s Workshop. We taught children to brainstorm, write, edit, and to publish their work in a finished product. When they were finished they had a story. The process was cumbersome and the stories the children produced were well, childish, bland, flat, and predictable. Being hindered by their lack of knowledge, the grammar and vocabulary was simple. But the product did not matter so much because what really mattered was the process, right? Charlotte Mason had a very different perspective. She called the practice of teaching young children composition an educational futility. 

“I think this great moral teacher here throws down the gauntlet in challenge of an educational fallacy which is accepted, even in the twentieth century. That futility is the extraction of original composition from schoolboys and schoolgirls. The proper function of the mind of the young scholar is to collect material for the generalizations of after-life. If a child is asked to generalise, that is, to write an essay upon some abstract theme, a double wrong is done him. He is brought up before a stone wall by being asked to do what is impossible to him, and that is discouraging. But a worse moral injury happens to him in that, having no thought of his own to offer on the subject, he puts together such tags of commonplace thought as have come in his way and offers the whole as his 'composition,' an effort which puts a strain upon his conscience while it piques his vanity. In these days masters do not consciously put their hand to the work of their pupils as did that 'prodigiously well-read and delightful' master who had the educating of George Osborne. But, perhaps, without knowing it, they give the ideas which the cunning schoolboy seizes to 'stick' into the 'essay' he hates. Sometimes they do more. They deliberately teach children how to 'build a sentence' and how to 'bind sentences' together.” vol 1 pg 244-245

She explains that to expect original thought from a child is to do him great injury and frustrate him because you are asking the impossible.  She goes on to explain that composition comes naturally and therefore does not need to be taught formally.    

'Composition' comes by Nature.––In fact, lessons on 'composition' should follow the model of that famous essay on "Snakes in Ireland"––"There are none." For children under nine, the question of composition resolves itself into that of narration, varied by some such simple exercise as to write a part and narrate a part, or write the whole account of a walk they have taken, a lesson they have studied, or of some simple matter that they know. Before they are ten, children who have been in the habit of using books will write good, vigorous English with ease and freedom; that is, if they have not been hampered by instructions. It is well for them not even to learn rules for the placing of full stops and capitals until they notice how these things occur in their books. Our business is to provide children with material in their lessons, and leave the handling of such material to themselves. If we would believe it, composition is as natural as jumping and running to children who have been allowed due use of books. They should narrate in the first place, and they will compose, later readily enough; but they should not be taught 'composition.'

Oral narration is the first step to becoming a good writer.  A child of six that is asked to write a composition of any kind is hindered by his lack of writing skills.  He does not know how to spell nor understand punctuation and grammar.   The forming of his letters can become a hindrance as well.  As a result the child must limit his composition to fit his limited skills.  Let him compose orally and you have just removed all of the obstacles to successfully communicate his ideas.   When a child narrates he is telling back what he knows from an experience he has had, a reading selection, nature observation, or picture observation.  When he tells back what he knows from a chapter in history or literature he will incorporate the grammar and vocabulary from the selection read.  As he gets older he will learn to add connections he has made or his thoughts and opinions into his narrations.  If you are presenting the child with living books written by authors using rich language and complex sentence structure your child’s narrations will eventually reflect that which has been model.   It follows that if you are presenting the child with dry, uninspired text books, his oral narrations will reflect the writing modeled in those books.  At the age of 10 or 11 the child will begin composing written narrations.  By this age the child will have spent extensive time reading and listening to models of good writing and are far better equipped to write than a child of younger years. 

There is wisdom in Charlotte Mason’s writings on this topic.  I can see there is also truth in it.  Let your child compose, orally, everyday with all of his books.  Just be sure those books are of a high quality with vital ideas and a rich vocabulary written by one author who is passionate about his subject.