Re: Au pair - how do i quit?
Personally, I find Odile's advice well taken. It can be hard, once you've fixed your sites on going home, to reconsider. But you've invested quite a bit to come here already; perhaps there is another family or option in Switzerland?
That said, in the spirit of Corbets' response, I offer my middling but adequate translation:
"J'ai demissione ma poste comme au pair, et je vais quitter la Suisse definitivement. J'ai l'intention de partir le xx decembre."
(This keyboard doesn't have accent marks, but you need to put an accent aigu [slanting up to the right] on both E's in demissione and the first E in both definitivement and decembre.)
(Fellow Forumites: any corrections welcome!)
Translation: I've resigned from my position as au pair, and I'm going to leave Switzerland permanently. I plan to depart the xx December."
This being Switzerland, don't miss the chance to make it an official document for the files: I suggest you write it as a real letter, with your name and Swiss address up top, your city and date on the upper right, address it to Office de la population, your city, its address. Open "Chere Office de la population," and close it "Avec mes meilleures salutations," .
I further suggest you give a copy of the letter to your employer-family, along with whatever documents the population office provides.
Good luck with this difficult transition!