Out of Time — Chris Archer

In the ninth book of this middle grade sci-fi series, teens time travel to find the scientist who can help them save their home planet.
 
Ethan, Ashley, Toni, and Jack used to be ordinary junior high schoolers in a small Wisconsin town. Until they turned thirteen and developed superpowers, a genetic inheritance from the Alpha race who gave them life. But their Alpha parents disappeared before they could protect their children from the Omegas, a mutant race determined to do away with any remaining Alphas and take complete control of Earth. So now the teens have to finish the job their parents couldn't. Time traveling to the past, they locate the scientist who created the Omegas, hoping to change the past for a better future. But finding the scientist is one thing. Convincing him to undo what may have been his greatest genetic engineering experiment is quite another. But then again, these are no ordinary teenagers . . .