The Field Guide by Tony DiTerlizzi
Book 1 of The Spiderwick Chronicles in which Mallory, Simon and Jared get acquainted with their new home but find many unexpected things. It all started when Jared Grace found their great uncle's book, "Arthur Spiderwick's Field Guide to the Fantastic World Around You" and they realise that are not alone in their new house. Now the Grace kids want to tell their story but the faeries will do everything to stop them...It's up to you to spread the word about their discovery. But heed their warnings, wear some red, turn your clothes inside out - all anti-faerie devices - and get ready to enter a world that you never knew existed...It's closer than you think...Their world has arrived!