The Littles Go Exploring

Tiny family. Huge adventures. Grandpa Little disappeared many years ago. Everyone says he is probably dead...except Granny Little. But when Tom and Lucy, the littlest Littles of all, find a secret room filled with papers belonging to Grandpa Little, they think that maybe he's alive after all. If the Littles read his diary and study his maps, can they find Grandpa Little or will he be lost forever?