Developmentally... ALL children go through and have general "fears" of which many of it comprises of night time, fears... the dark, monsters, night time noises, shadows etc.
Some kids, start to have night fears from 2 years old.
EVEN my 9 year old daughter, will still get scared at night of things at times.
Things that to an adult, is silly or not realistic.
But to a child, they go through this.
A child's mind/cognition/imagination... ALSO goes through changes and more development. And we certainly cannot turn "off" a person's imagination. And at this age they do not comprehend abstract things nor the rationale that adults have.
Even myself as a child, I got this way but was older than your son.
My parents, just knew it was childhood things and they never forced me to not be scared.
I slept in my parents bed too... I would creep down our LONG dark scary hallway JUST to be near them. I was close to them. They let me. They got sleep. I got sleep. They did not battle about it. They knew... I would grow out of it and I did. They never told me I was just manipulating them. I was not. But my other sibling, would make fun of me... but she was never close to my parents and was a cold individual.
This is NORMAL.
All kids, go through this.
He will grow out of it.
Also at this age, a child has nightmares. So that scares them too.
For me, I comforted my kids during bouts of this.
We'd take them outside with a flashlight to explain the nighttime noises they heard from outside. We told them its okay, they are kids, kids go through this. We let them keep a flashlight in their bed with them. And TONS of loveys in bed with them too.
Ask your parents, if you ever got afraid of the dark as a child or not?
Most kids do go through this. It reflects their changing developing cognition/imagination.