Hi Christine,
As a former au pair I thought I'd weigh in on your question.
I'm South African and au paired with a family in MI in 2000 through Au Pair in America/AIFS. I was 24 years old when I took a 'gap year' after finishing school. I chose to become an au pair because the idea of a cultural exchange appealed to me, I wanted to spend some time abroad, and obviously I liked children too.
I had an amazing experience. My host family always joke that I interviewed them - I had about 4 pages worth of typed questions, double spaced, and turned down 4 families before accepting the one I ended up living with. After my au pair year I chose to continue traveling and lived in London, UK, before moving back to MI after being offered a position on staff at a local church. That's when I met my husband and how I ended up settling in the States. I am close with this family to this day. Their daughter now goes to school at Northwestern in Evanston, very close by; we see this family at least a few times a year in MI, my host mom was my matron of honor, etc etc.
As you explore hiring an au pair I hope you will consider the following, especially as some responses below were a bit disconcerting: in particular comments about the 'negatives' including feeding the au pair, giving her privacy, and not being able to work her over 45 hours a week.
It is cheaper to have an au pair than a nanny, perhaps, but either one has financial considerations and with anything you have to decide if it's something your family can afford. You are inviting a person to live in your home 'on par' with you as a member of the family. You are not hiring a servant. Most of the girls are coming into the situation assuming this, and I think then you will get the most out of your relationship anyway. And the actual money an au pair receives is very little - it's pocket money basically. It's not for her basic necessities like room and board, and honestly, gas to ferry your kids around (or anything else that she has to pay for in relation to caring for your children.) That is part of what she is working for - she is being paid 'in kind'.
She is also an adult - how would you feel if you had to share a room, or never have any space/privacy? I don't see how this should be considered a negative. It's just respect, and again, part of what she is working for.
Finally, working 45 hours a week is perfectly reasonable. Again, that's part of the cultural exchange experience - the girls aren't coming over to experience only living in your house - they need time and space and opportunity to rest, explore the city they've come to, make friends, etc. If you expect more than that, you run the risk of taking advantage of someone who is already in a somewhat vulnerable position of having left her own country and entire support network. I did sometimes work overtime, but it was pre-arranged, I never was made to feel obligated, and I was paid an additional hourly rate competitive with adult babysitting fees.
Naturally, part of picking the right fit for your family will require careful thought and questioning during your interview process. As was mentioned by some folks, of course there will be some immature and irresponsible people coming through ANY program.
Your intentions and motivation to establish a relationship of mutual respect, an openness to truly care about this person, and the willingness to set healthy boundaries for both yourselves and for the person you're welcoming into the family will all go a long way in making the au pair experience a truly wonderful one for you and your children and will hopefully create the opportunity for some life long friendships.
All the best to you!
N.