Almost certainly, such achievements will have come when you have invited your kids to reflect upon their own significant experiences. Imagination first, then the effort of structuring, of composing, and finally of execution - all for you, or for some other trusted audience. The real problem is to show them how they can distance themselves sufficiently from their own experience to be able to have access to it, to be able to structure it, to get sufficiently far away from its immediacy to be able to grasp it. We have to meet them as person to person, and we have to learn to make as few judgements as possible about what they offer - and what they offer can, at time s, be very disturbing. Teaching at this level is the teaching of individuals.
Writing is the biggest stumbling-block.
Language use, in the most general terms, is not the problem which it might appear to be - witness the vivid oral command which these children often have. They love to talk, so start there. Mountains of discussion and oral activity. Gradually cut back your intervention and control, and they will slowly become self - sustaining. Oral work is a powerful tool in helping them meet one of their first needs - that of composition, of structuring their experience.