It really depends, every child is different especially in age group, I’d suggest starting with the basics and having them tell you a story and if they’d want to add illustrations let them draw it out like a picture book. At the beginning it’s better to small with short stories, if anything a small paragraph. It’s a skill or habit you want to start out small with and then build. Show your interest in it as well, you can both write and story and share or you can listen to their story and be the one to draw the illustrations. Younger children do better when they have someone being hands on with them so they have someone to talk to be it feedback or figuring out how the story should go. When it comes to older children, sometimes a dairy is a good start or a notebook where they can keep knickknacks like pressed flowers or random flyers maybe even stickers. Writing needs to be nurtured and done in an interactive way to get the students to follow or take part in.
Let me know if you’d like any other suggestions or
ideas. You’ve got this!