[null and void]

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.”

[NoCmpromiz]

Timmy?

[Telepathic Intruder]

There's a Far Side cartoon, I couldn't find it at all online, where a kid is in bed looking scared while two monsters are underneath, one saying "I've got it again, Larry...an eerie feeling like there's something on top of the bed".

But in lieu of that, this has got to be my favorite one: