Wholesale Era of Great Wonders by John Myers

[Source Point Press] In a single day, unimaginable monsters appeared on Earth and turned the cities into their personal battlegrounds. Years later, the survivors tell their stories. The Era of Great Wonders began in a single night. Without warning, giant monsters from beyond imagination appeared, turning the great cities into their personal battlefield. But among the ruins the survivors struggle to build new lives: soldiers, bandits, and normal people just trying to make it to the next day. In the midst of it all three children discover a chance to become heroes and change the history of their world forever.