Flag 9, Book 3: The Wiccademous by A. G. Rives

For twelve year old Zach Moore, moving to Amelia Island was supposed to be a fresh start, a chance at a new life. But across from his new school, there is something in the woods. A legendary witch resides there. Teaming up with new found friends, they go to investigate, and soon discover that messing around with the Wiccademous can have very unexpected consequences.