Child at Heart/Fallout 3

Child at Heart is a perk in Fallout 3 that was also cut from Fallout: New Vegas.

Fallout 3
The Child at Heart Perk greatly improves your interactions with children mainly, but some adults and, strangely, a robot, usually in the form of unique dialogue choices. The Child at Heart perk is particularly useful in Little Lamplight, where a lot of children are present.

Additional dialogue options

 * Mayor MacCready will allow you access to the town as well as give permission for you to trade Buffout and strange meat for cave fungus.
 * Biwwy will give you the Wazer Wifle for free (or "fwee").
 * Eclair will trade with you (he has cave fungus for around 50 caps each).
 * Knick Knack will trade his goods with you at a discount.
 * You can convince Zip not to shoot you.
 * Maggie in Megaton will tell you the combination to Billy Creel's safe.
 * Bryan Wilks, near or in Grayditch, will give you the key to his father's weapon and ammunition stash.
 * Rachael, Ralph and Flower will let you enter The Republic of Dave.
 * James Hargrave in Rivet City will steal ammunition for you.
 * Derek Pacion in Canterbury Commons will tell you the weaknesses of the AntAgonizer and the Mechanist. You can then convince them both to stop fighting after passing a speech check.
 * Dean Dewey in Roosevelt Academy will ask you for a hallpass once he is activated at a terminal. You can convince him that you forgot your pass with this perk and he will not turn hostile.
 * Penny in Paradise Falls will be convinced to leave Rory McLaren behind during Rescue from Paradise.
 * The Mechanist will be convinced to stop trying to be a hero when the player reminds him that his actions are putting Derek Pacion in danger.
 * Sapling Yew in Oasis will tell you Harold's fear (fear of fire, or rather burning to death) and will give you Yew's bear charm upon completion of the quest.
 * Machete in Canterbury Commons will acknowledge that she was on her way to Big Town but decided she'd rather explore and ended up where she is now.
 * Croatoa in Point Lookout will give you the fertilizer shovel.
 * Kenny in Point Lookout will allow you to store your gear and sleep in his cave without having to search for and return his Kenny-Bear.
 * Midea in The Pitt will disclose Wernher's location during Free Labor.
 * Sally on Mothership Zeta will take you to a hidden stash in the engineering core through an otherwise impassable forcefield.

Fallout: New Vegas
This perk exists as unimplemented content in Fallout: New Vegas and there are a few uses for it hidden in the game's code, but because there are very few children in the Mojave wasteland it was left out.

Bitter Springs refugees
Regardless of which greeting you hear, you will receive Barnabas Bear.

Lindsay
Lindsay is the Mini Boomer at Nellis AFB who is missing her teddy bear, Mr. Cuddles.

Max
Max is the boy in Freeside who chases his friend around with Euclid's C-Finder.

Melody
Melody is the slave girl at the Fort.