David Miller 
Shark Island 

Hanna, Ned and their parents are on the holiday of a lifetime on the paradise island of Kaitan. But the idyll is shattered when pirates come in the night, burning their house and kidnapping their mother and father. The children are stranded, and don’t even know if their parents are alive or dead . . . In this action-packed adventure, there is no one to help. Survival and escape are up to Hanna and Ned.