Alive by Scott Sigler

Savage awakens in a coffin and smashes her way out. She discovers five more people still alive, but six others are bony corpses. Even though they all say it's their twelfth birthday, their clothes are way too small, and they look like twenty-year-olds. Savage is chosen leader of the group, and she leads them through endless hallways scattered with broken skeletons of adults, kids, and babies. She figures it's safest to continue in a straight line, and they eventually meet a group of two dozen other boys and girls who've been awakened. They keep walking and find a room full of plants, water, and food, but one girl is killed and eaten by wild pigs. Another girl is captured by strange creatures, with dark wrinkly skin and red eyes, so Savage leads the group away into a nearby hallway. They are shocked to find themselves back with the same coffins where they first awakened. How is this possible if they walked away in a straight direction hours and hours ago? The truth will make them rethink everything they thought they knew.

The plot jumps into the action right away, as Savage finds herself trapped in the coffin. She hears voices in her mind, but it's obvious she has hidden memories that will be revealed as the book moves along. Savage is a reluctant leader, but she's better than the other choices. Bishop is a muscular, impulsive young man, and he presents an ongoing challenge to Savage's character. The relationship between the kids and the dark creatures is creative. The plot unfolds like a mystery, but the action and suspense are riveting. The author has told me that I shouldn't give away too much information, so I'll let you enjoy making your own discoveries!