Tuck Me In (1:00)
Ignacio Rodó; IMDb; Vimeo; YouTube

A little boy asks his father to tuck him in bed. Then he asks him to look under the bed. What he sees... I don't want to spoil it, but it's pretty unsettling.

Actually, I guess this is based on a two-sentence short story I read online at some point in the past, and this is just one of several short films that have been based on it. I had forgotten about the story until I saw this film, though, and started trying to figure out why it seemed so familiar.