Lost on the Mountain — Mark Thomas

Sam Brooks and his younger sister, Sara, have suddenly found themselves lost in a vast mountain wilderness. Sam has never thought of himself as brave. After all, just last week, two neighborhood bullies made a fool out of him. And before that, his stepfather used to kick him around. But now, darkness has fallen and the woods are alive with terrifying dangers that Sam has never had to face before. He has no choice -- Sam must be beyond brave if he and Sara are going to survive.