Face the Fear — Chris Archer

In the eighth book of this middle grade sci-fi series, superpowered teens must save the Earth's future from dangerous mutants by traveling to the past.
 
Trapped on a futuristic Earth, Ethan, Ashley, Toni, and Jack must battle earthquakes, giant rats, and a ruling superhuman race of Omegas, in order to stay alive. And failure is not an option, as the teens might be Earth's only hope to return to the haven it once was. The plan? Dodge the Omegas and the quakes -- and the huge rodents -- long enough to make it back to the time machine that got them here in the first place. If the gang can make it back to the past, they can create the kind of future on Earth where they -- and others like them -- might actually want to live.
 
Their mission has one pretty major complication. The time machine is located in the Omegas' headquarters, and the only way to get to it is to step right into the hands of the enemy.