I begin tucking him into bed and he tells me, Daddy check for monsters under my bed. I look underneath for his amusement and see him, another him, under the bed, staring back at me quivering and whispering, Daddy there's somebody on my bed

Don't be scared of the monsters, just look for them. Look to your left, to your right, under your bed, behind your dresser, in your closet but never look up, she hates being seen.

The dark is generous, and it is patient, and it always wins. 
It always wins because it is everywhere. 
It is in the wood that burns in your hearth, and in the kettle on the fire; it is under your chair and under your table and under the sheets on your bed. Walk in the midday sun, and the dark is with you, attached to the soles of your feet. 
The brightest light casts the darkest shadow