Make sure the concept you are dealing with is a childlike concept, not an adult one. Many people want to write for children because they don’t like the way young people behave. This is a mistake. You must love children to be able to write for them.
Use as few words as possible when writing for children and use words that are in their vocabulary. Write concisely in all your writing, but particularly here. Write concretely, with step-by-step instructions or events. Have your story follow a logical, sequential order, avoiding flashbacks. They are hard for children to follow.
Your story should teach a lesson, without being preachy. If you try to tell your young audience what to do, they will tune you out. Yet, they can learn a great deal from your characters, climbing in their skin and experiencing what the characters experience, learning the same lessons along the way.
I have found that writing for children is much harder than writing for adults.