We've used Au Pair in America (https://www.aupairinamerica.com/), but we are currently using Cultural Care (https://culturalcare.com/). I don't have particularly strong feelings on either in general, but we switched because our local coordinator had gotten pretty flaky.
I don’t have any kids and don’t plan on having any. Just wanted to thank you for such a detailed explanation of what an au pair is. Also, I’m in the Bay Area too. Oakland. Hi neighbor.