The Secret of Eel Island (2005)

When Scott moves to a new house opposite the mysterious Eel Island, he can't wait to explore. Once home to the secretive Eel Catchers, the island is now apparently deserted, although rumours abound of the ghost of a little girl who guards its shores. But Scott discovers the last inhabitant of Eel Island is no ghost when he comes face to face with eight-year-old Sapphire, a fiercely free spirit, quite unlike anyone he's ever met. Together, in a world hidden from adults, they'll share many adventures as they fight to protect the Secret of Eel Island.