Jonny's in the Slag caves. Find a way to get Jonny back home to Balthas

 is a side quest in Fallout 2.

Walkthrough
You found Jonny in the Slags' underground cistern. Now, you need to prove that you're here to take him home. To do that, don't pick the creepy "Want some candy, little boy?" line, and tell him that his father Balthas wants him to come home.

He'll tell you to speak with Vegeir, the Slag leader.

None shall pass
Vegeir won't let you take Jonny home until the Modoc situation is resolved. Find Karl, and calm Jo's fears. Then, and only then, Vegeir will give you, Laddie, and Jonny an armed escort back to Modoc.

Reward

 * No official reward, but you do get the rewards for Jonny is missing. Find him and bring him home to Balthas.