Will the au pair be using the car the drive your children around? If so, I’d focus on safety, dependability and having enough room for your children + their gear. Maybe a Honda Odyssey.
What are you going to do with the car when your au pair leaves / you no longer need au pairs? If you are going to continue to use the car - maybe you would have a teen driver by that time - I’d focus on longevity and ease of maintenance. Maybe a Honda Accord or Toyota Camry.
If this car is strictly for the au pair’s use, I’d do a used car with low insurance rates. For me personally, especially in this climate where cars are being sold for way over MSRP and used cars are grossly overpriced, I personally wouldn’t spend more than $10k over a car only for the au pair. But the sky’s the limit…. My au pair told me that another family “gave” their au pair a Tesla Model X. Lmao.