iPhone video has no sound

I feel like a fool for not knowing how to fix this, but either there isn't a way, or it's something simple and I'm an idiot.

My wife loves taking videos of our kids with her iPhone. Everything's has been fine. Yesterday - fine.

Son got ahold of the phone today and we thought nothing of it. Videos were taken of the kids trick-or-treating. All videos have no sound. Videos taken NOW have audio. The videos in question have the little speaker greyed out and can't be toggled. Is the sounds gone?

Things we have tried:

Turn off and on.

Hard restart.

Reset all settings.

Updated the phone.

Sent the video to my phone by messages.

Sent to my phone by airdrop.

Casted to Apple TV.

Emailed video.

All scenarios play the video without sound.

Not sure what happened today while trick-or-treating but they are the only videos like this. What haven't I tried? Is there any way to see if audio is present and just not playing?

Any help would be magnificent for my wife.