A storm at 3pm is an event. A storm at 9pm is an event happening to a child who is also supposed to be falling asleep, which is a much harder thing to do.
The official guidance on what actually makes a location safer during a thunderstorm, including what to do if you are caught outdoors.
Download the PDF ↓Check the current version on Ready.gov →A U.S. government work, free of copyright. We host a copy so you can have it immediately, and link the live version too, because an emergency document that has been updated matters more than a convenient copy. We are not affiliated with, and not endorsed by, FEMA, DHS or any government agency.
Counting the gap between the flash and the sound turns an unpredictable noise into a countable one, and countable things are less frightening to a young child than random ones. It also gives you both something to do together in the dark.
If a child cannot settle in their own room during a loud storm, moving them somewhere calmer for the night is not a habit you are creating — it is a reasonable response to a loud night. One storm will not undo months of a normal bedtime routine.
Go back to the same bedtime steps you always use. The storm was the disruption; the routine returning to normal straight after is what tells a child the disruption is actually over.
For most children, yes, as they build up enough calm experiences of storms passing safely. A specific, ongoing fear that is not easing over time is worth mentioning to a paediatrician, but an occasional bad night is not that.
That is a judgement about your home and the storm itself, not something we would presume to answer generically - the official sheet linked below covers what actually makes a location safer during a thunderstorm.
Part of our guide to Talking to kids about emergencies.