Structure without supplying the story
Ask what changes, not what is supposed to happen.
Beginning, middle, and ending can describe how a story changes rather than a formula the child must fill in correctly.
Beginning: what is true before the change?
Ask where the character is, what they are doing, or what they want. One clear situation is enough. The beginning does not need to explain every character or promise the kind of story that follows.
Middle: what becomes harder or different?
Invite the child to add a rule, disagreement, mistake, discovery, or choice that changes the original situation. If several surprising events appear, help connect them by asking who notices and what they decide because of it.
Ending: what can the reader see has changed?
The ending can show a decision, new relationship, solved or transformed problem, final joke, or quiet image. Ask the child what should be different from page one. Do not require a moral or a return to normal unless that is what the child wants.