"Inspector Gadget is always on duty!" The Fountain of Cortez is the first half of episode 17. It introduces Doctor Ithica Marvins who is pushed into the Fountain of Youth by Talon, who also splashes Chief Quimby with the water.
The babies are returned to adult form in the Basin of Aging when Gadget dunks Quimby and Penny dunks Ithica. Both are left in their diapers topless in the pool together.