L.S.
That could work....I've also heard of people giving their children clean spray bottles with "monster repellant" (water) and letting the child fumigate for monsters before bed.
Personally, I just tell my daughters that *I'M* scarrier than any monster and will kick their butts!! This usually gets them giggling and resets the mood to a happier one. Follow by some snuggles and lullabies and my daughters have only had a handful of nightmares between them.