There is a kind of child — and a kind of night — for whom a made-up story is exactly the wrong thing. Imagination, for an overtired four-year-old, can run in any direction, including under the bed. A true story runs in one direction only: toward how the world actually is. That turns out to be very soothing.

A fact is something to hold

The moon changes shape every night but is always the same moon. The sea goes out and comes back twice a day. Every snowflake has six sides. These are not plot points; they are handholds. A child lying in the dark with one true thing to think about is a child whose mind has somewhere calm to go. Fiction asks a child to wonder what happens next; a true story lets them wonder about something that has already, safely, happened.

Told, not taught

The difference between a true bedtime story and a lesson is entirely in the telling. A lesson lists; a story follows. A tiger cub who is nervous of the water is a story, and by the end of it a child knows that tigers, unlike most cats, swim. A story about young Marie Curie noticing that certain rocks glow in the dark is a story, and by the end of it a child knows a little about curiosity and a little about radium, in that order.

The rule for telling one: choose one true thing, and follow one character toward it. Leave the second fact for tomorrow.

Which true stories work at bedtime

Animals, first and always — how they live, what their bodies are for, the surprising thing they can do. The earth and the sky: rain, snow, the moon, the planets. Long ago: dinosaurs, mammoths, the first fire, the first wheel. And people, met as children: the moment Einstein daydreamed about riding a beam of light, or Harriet Tubman first followed the North Star. What they have in common is that they are about the world, and the world will still be there in the morning.

What to avoid: anything with a frightening true ending (the dinosaurs are fine; the asteroid, at bedtime, is not), and anything the child has a real worry about. The point of a true story at bedtime is that it is safe to be true.

When the story raises a question

True stories produce questions — why does the moon change, how did they know the Earth was round, what happened to the mammoths — and at bedtime the right answer is usually short and honest: one sentence, and "we can look that up tomorrow." A child does not need the whole explanation at nine o'clock; they need to know the question was a good one and that it will keep. Write it down if you have to. Some of the best mornings start with a question left over from the night before.

In the library

Most of the stories here are true — or true-hearted, in the case of the myths and the childhoods. The Animals, Earth, Space and History shelves are the place to start; When They Were Young is the one for a child who likes people.