Must....resist...temptation...to....give....away....the...plot...twist....I've....read....on...the....internet......
Think hard about what the "creatures" could be.
You were the kind of kid who searched the house high and low to try to find out what your Christmas presents were gonna be, weren't you? My kiddo is like that, and I've told him his whole life that he's robbing himself of the delight of a surprise. He can't stand the idea of not knowing what he's getting.
Nothing ticks me off worse than for someone to be sloppy about keeping secret what they've gotten me for a birthday, Christmas or anniversary present.