The Runaways

 refers to an unmarked quest in Fallout 3.

If you engage James Hargrave in Rivet City in conversation and bring up the issue about his equally problematic alcoholic mother, he gets angry. This leads to an option for you to insult and goad James into running away from home through a speech challenge. If successful this earns you Bad Karma and has repercussions - Rivet City residents and guards later report that C.J. Young (well-behaved little daughter of the Young family) has gone missing. You receive a note on the PipBoy indicating you as being possibly responsible for C.J. going missing.

One of the female Rivet City guards may tell you that she has on several previous occasions seen these two children running across the Rivet City Bridge which connects the ship to the dangerous mainland. You may chance upon this happening if located at Rivet City Bridge in the early morning.

When you find James and C.J. at Anacostia Crossing Station you can bring them back home. If you do so C.J. Young will be able to talk to the player.

Reward

 * -100 Karma then +100 Karma (+50 Karma twice successively)
 * Loss of the Light-Fingers Hargrave repeatable quest temporarily

Bugs
When playing with a lot of followers on Xbox 360, CJ and James will follow at the back. Which seems to mean they are too far away from the door to Rivet city to enter when you do, making this mission near impossible to do. Pushing them might work. (confirmed)