Glory

You won't personally get to see the delighted looks on kids' faces as they open the gifts you've hand-crafted, but you'll know they're there. And it'll somehow make all of the grueling hours for incommensurate pay well worth it.

 
And the ones who do think you exist? Well...let's just say it's best you keep your distance. (Source)

Actually, come to think of it, you've probably never seen a human child at all. What do you care if they're happy or not? Why are you slaving away to bring happiness to a race of ingrates who barely even acknowledges that you exist?

Er...um...yeah, so...you'll do it for the kids.