The Wee Free Men/Terry Pratchett

A nightmarish danger threatens from the other side of reality...Armed with only a frying pan and her common sense, young witch-to-be Tiffany Aching must defend her home against the monsters of Fairyland. Luckily she has some very unusual help: the local Nac Mac Feegle - aka the Wee Free Men - a clan of fierce, sheep-stealing, sword-wielding, six-inch-high blue men. Together they must face headless horsemen, ferocious grimhounds, terrifying dreams come true, and ultimately the sinister Queen of the Elves herself...This is The First Book In The Tiffany Aching Sequence.