From: Star Trek: Deep Space Nine
Caption: Odo teaches the changeling infant
Nameless young Founder that was found on Deep Space 9 in 2373. Fellow changeling Odo took the young lifeform under his wing and oversaw its early development. When the young changeling was about to die, due to overexposure from tetryon radiation, it managed to infuse itself into Odo, who in turn regained his shapeshifting abilities.