Jumble Joan by Rose Impey, 1989.
A boy and his friend, Mick, take his little sister upstairs to explore their grandmother’s attic one evening. The boys are hoping to scare the girl by telling her all sorts of creepy stories about the stuff they find in the attic, but if they’re scaring anyone, it might just be themselves.
A rocking horse becomes one of the dreaded “Ten O’Clock Horses” that might drag a child off into the night if she isn’t in bed on time. An old stuffed parrot in a cage becomes “The Deadly Vampire Bat”, waiting to suck their blood. But, the most sinister creature of all might be “Jumble Joan”, who hides by pretending to be a pile of old clothes, ready to steal away any little girls who might want to play dress up in their grandmother’s attic!
Although the brother narrates the story, the pictures show that his little sister knows exactly what the boys are trying to do, and she does things to turn the situation around.
This is one of the books in the Creepies Series. Kids under the age of seven might find stories in this series a little scary because they focus on how stories about monsters can build in the imagination, even if you know that you made them up yourself. Still, all of the books have good endings, and this one is pretty funny.