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.
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.
Penny in Paradise Falls will be convinced to leave Rory McLaren behind during Rescue from Paradise.
You can convince him that you forgot your pass with this perk and he will not turn hostile.
Dean Dewey in Roosevelt Academy will ask you for a hallpass once he is activated at a terminal.
You can then convince them both to stop fighting after passing a speech check.
Derek Pacion in Canterbury Commons will tell you the weaknesses of the AntAgonizer and the Mechanist.
James Hargrave in Rivet City will steal ammunition for you.
Rachael, Ralph and Flower will let you enter The Republic of Dave.
Bryan Wilks, near or in Grayditch, will give you the key to his father's weapon and ammunition stash.
Maggie in Megaton will tell you the combination to Billy Creel's safe.
Knick Knack will trade his goods with you at a discount.
Eclair will trade with you (he has cave fungus for around 50 caps each).
Biwwy will give you the Wazer Wifle for free (or "fwee").
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.
The Child at Heart perk is particularly useful in Little Lamplight, where a lot of children are present. 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.