**Help him feel safe first; keep the explanation brief.** A child can understand that a story is invented and still feel frightened when the lights go out. Childhood fears are common, and sympathy and gradual practice are more useful than pressure to be brave. [American Academy of Pediatrics](https://www.healthychildren.org/English/health-issues/conditions/emotional-problems/pages/Understanding-Childhood-Fears-and-Anxieties.aspx)

You could say:

> “That story really frightened you. Slender Man is a made-up character. Sometimes our brains keep sounding a danger alarm after a scary story, even when we’re safe. I’ll help you get comfortable sleeping here again.”

I’d drop the discussion of why he collects children or how teleportation might work. Those questions invite more speculation about the character. Also, copying and transporting a person is not an established scientific capability; you don’t need that qualification to explain that the story is fiction.

Try this approach:

- **Talk during the day.** Listen to what specifically worries him—being alone, a window, a shadow—without ridiculing it or repeatedly debating the monster’s powers.
- **Make a bedtime plan together.** Use a familiar, pleasant routine, a nightlight or open door if helpful, and a comforting book. Practise a few slow breaths together.
- **Reduce your presence gradually.** Initially sit nearby while he settles; as that gets easier, move toward the doorway, then use brief, predictable check-ins. Choose manageable steps together and praise his effort, even if he still feels nervous. Gradual approaches are recommended for childhood fears. [American Academy of Pediatrics](https://www.healthychildren.org/English/health-issues/conditions/emotional-problems/pages/Understanding-Childhood-Fears-and-Anxieties.aspx)
- **Help him set a boundary at school.** Rehearse “I don’t want to hear scary stories.” If the other child keeps frightening him deliberately, involve the teacher. Avoid further frightening videos or searches for now.

You cannot prevent every fright, but you can help him learn that frightened feelings pass and that he can cope with your support. Regular routines, listening, and simple relaxation are consistent with [NHS guidance on childhood anxiety](https://www.nhs.uk/mental-health/children-and-young-adults/advice-for-parents/anxiety-in-children/).

If the distress persists, worsens, or substantially disrupts his sleep or daytime life, speak with his pediatrician or a child psychologist. You can seek help sooner if he is already struggling badly.