It's not time-reversal, because they're still on the airship and they remember everything. It's a mass de-aging spell? Not sure what that accomplishes unless you leave some of your guys as powerful adults. Gonna go out on a limb and predict Lara's true goal was to recreate her happy childhood with Olivia and Lana.
Horrible thought, what if it de-aged some of the kinds out of existence?!
More importantly, tiny triceratops guard with a belly button!