Now I Lay Me Down to Sleep (SF)

From the introduction:

No one can be sure if household spells are the origin of more powerful magic or intentional mimicry of the tools of legendary heroes. Some point to the similarities between the verbal components and prayers whispered by parents as they tuck in their children. Others suspect the same capricious fey the wards were meant to repel were responsible for spreading and developing the powerful magic. But as adventurers travel miles from home, they find the same terrors that went bump in the night threatening the very balance of the cosmos. And the prayers and stuffed animals that protected them when they were dewy-eyed children are the same weapons that will save the world from the encroaching darkness.