The best thing to do with children under six to introduce them to narration and lay the ground work for the formal narration they will begin in school is to simply be a good listener--listen to them tell about their day, their time at a friend's house, the dinner they had, what they did with Daddy while you were out, what they saw while they were outside playing. Gently, simply, and organically help them to build their observation skills in the context of everyday life. Perhaps they will even want to tell back a book you have read to them. Of course, allow them to do this but also never force a narration.
Around six is when formal schooling begins. This is when the formal reading of a story and the asking, "Tell me what you heard," commences. The child no longer has the option to narrate or not to narrate. Ideally, every book which you read in the context of school will be narrated. Some children will just take off and enjoy narrating, telling back in great detail everything they have heard. Others will not. Sometimes it will take a year, or more, of this early work for a child to really develop the skill of narration.
So how do we approach those who will not? Gently. Read short passages, maybe a paragraph. For a harder story, as not every book will be received the same way by the child, you might only read a few sentences before you ask the child to narrate. Accept whatever the child might have to say except, "I don't know." It is OK if it is just one idea or thought. If your child is struggling, take turns and model the narration for the child. Remember to keep lessons short and varied. If you have been reading and narrating for fifteen minutes, it is time to set it aside for awhile and turn to something new.
Do not moralize the readings for the children. Simply read and narrate. If, after narrating, a child on his own has a good question or thought, that is great. But, if after narrating, they have nothing to add--perhaps the story really was just about a lion and an ass and they don't see the inner layers--that is OK, too! Send them on their way to play outside. If the child is not seeing what you see and not getting what you get, don't force the lesson by expecting them to have your same relationships and connections with the stories.
But children will not take in all this? No; but let it be a canon that no story, nor part of a story, is ever to be explained. You have sown the seed; leave it to germinate.
Miss Mason, Volume 5, p. 216
Perhaps you are just now making the transition to a CM education after having used something else for a year or two or even more. It does not look much different than what you would do for a child who has started with CM from the beginning. Introduce narration slowly and gently. Accept short answers, model when needed, and don't force a conversation by wanting a child to make the connections you are making. The child should be narrating everything you have chosen for a school book, so if there is a quite a struggle with this transition, cut back on the number of books. Focus on learning the skill.
Feel free to use a drawn narration as a treat. At this point (and actually throughout the whole of their education), their main narration diet should be oral narrations. When you do have your child do a drawn narration, make sure they are still giving an oral narration by telling about what they have chosen to draw. Again, "That is the lion and the ass," is a lovely answer.
I'm not going to address written narrations in this post, as a child typically does not start written narrations until Form 2 or about the age of 10. And even if you have an older child new to narration, you would not want to start written narrations until he has a solid handle on the skill or oral narration.