I separated the cost issue so it wasn't lost in the other wall of text.

I use a DCFSA (https://www.fsafeds.com/explore/dcfsa) to pay for it. Au pair expenses are a valid expense for this. Our marginal income tax rate is around 35%, so this helps a lot.

  Without DCFSA:
    Pre-tax Cost:  ~$32,300
    Post-tax Cost:  $21,000

  With DCFSA:
    Pre-tax Cost:   $21,000
    Post-tax Cost: ~$13,650

This is all an estimate of course (like increased insurance or rent on a larger place can't be paid for using a DCFSA), but it makes the point. So I think of the cost as around $13,650 for 45 hours / week, 50 weeks / year, 2250 hours in total. No matter how many kids you have.

If that big chunk is hard to swallow, the agency fees are ~$8000, and most agencies will let you break that up into a payment plan. The au pair is paid $200 each week, so that ~$10,000 is naturally spread out. The remainder is what we estimated our additional costs to be, like food, insurance, etc. and that gets spread out as well.

The doc we share is pretty long, but it can be broken down into:

  - Welcome Message
  - Basic Information about the Family
  - Details about the kids
  - Health and Safety
  - Au Pair's Responsibilities
  - Sample Schedule
  - Basic House Rules
  - Pay and Vacation
  - Driving
  - Other Perks
  - Law & Safety
  - Guest Policy
  - Reasons We Would Ask You to Leave

Like I said, our issues have usually revolved around trust, but we have also identified a few things that are hard rules for rematch:

  - Drunk driving (we encourage them to take a cab or call us for pickup)
  - Hard drugs
  - Abuse of anyone, especially the kids and pets.
  - Neglect
  - Repeatedly not caring for the children when it’s their responsibility
  - Outright lying to us.

The other rules that really matter to them are:

  - No taking the car more than ~60 miles without prior approval and you pay for a service appointment. 

When an au pair has free use of a car, other au pairs in the area pressure them to be the driver for weekend road trips. We had one au pair put 30,000 miles on the car in a year because of this.

  - If you're going out for the evening let us know roughly where you'll be and when you'll be back, and keep your phone charged. 

We had one au pair that didn't tell us anything about where she was going, only a rough estimate of when she'd be back. At one point she didn't get home until 36 hours after she told us she'd be back. We had been calling police and hospitals in the area because we were worried about her. It turned out she had gone to a club with friends, met another girl there, the other girl offered to drive her home so the friends left, then on the way home the other girl suddenly deviated and went to a house party on Treasure Island (in the middle of the San Francisco bay) and then proceeded to get completely wasted leaving our au pair without a ride. She hadn't charged her phone and it was dead, so it took her a while to be able to get home. This ended up being a big fight about how she was an adult and could make her own decisions. It abruptly ended when we pointed out we didn't care exactly where she was or what she was doing, we just needed to know which hospitals to call if she didn't ever come home. She actually radically changed her behavior after this and we didn't have any more problems.

  - Don't use the phone for international calls, use Skype or Zoom, or WhatsApp. 

We didn't have a problem, but we knew a family that got hit with a $5000 phone bill because their au pair was spending every minute on the phone with family in Italy.

  - The au pair gets two weeks of vacation, but if we can select one of the weeks then they get an extra week. 

This isn't a hard requirement, but we've never had an au pair turn it down. Our kids stay with grandparents for two weeks each summer, so the au pair gets those two weeks off and it only costs them one week of vacation.

That's the important stuff. It's always easier to make the rules looser, so we start off on what we feel is the strict side and then loosen them up over time, especially as we get to trust them more.