Their World Is Closer Than You Think

When the three Grace children, troubled Jared; his bookish twin, Simon; and their sister, Mallory, move to the ancient Spiderwick mansion, they are at first none too enchanted by the rundown Victorian until they discover a Brownie, an enchanted creature, living in the walls.
They soon find a book, Arthur Spiderwick's Field Guide to the Fantastical World Around You, that will open their eyes to the invisible, odd, and sometimes dangerous world of dragons and boggarts, phookas and fairies, sprites and goblins that is all around them. When they cross paths with Mulgarath, an ogre, they realize quickly that he will stop at nothing to get his hands on the Field Guide.
Based on the bestselling series of books by Tony DiTerlizzi and Holly Black.