The movie I am looking for was about a little boy who was afraid of the dark because of the fact of a monster living under his bed... one night during a lighting storm thre was a light that was shining he looks under his bed and is swept away to a world where humans are feared and it is full of monsters. And he has to rush back to his world before day or he'll be stuck there forever. Does anyone know this one?

Little monsters with ben savage

Little Monsters (1989) (http://www.imdb.com/title/tt0097758/)

You know what, little monsters isn't animated though. But your description fits.