The Field Guide by Tony DiTerlizzi

The Spiderwick Chronicles, Book 1

Three siblings, Jared, Simon, and Mallory Grace, move into a dilapidated old mansion with their mother, only to discover a mysterious book that unveils the hidden world of faeries and magical creatures. As they delve deeper into the secrets of their new home, they encounter both wondrous and dangerous beings, leading them on an adventure filled with enchantment and peril. The siblings must navigate this newfound reality, relying on their courage and wit to protect themselves and their family from the mystical threats that lurk in the shadows.