We always give our AP’s the option of joining us on our family vacation. We’ve had 3 Au pairs (who all extended with us, one for 2.5 years during COVID), and none of them have turned down our offer to join us on vacation (I’d actually prefer if they turned down the offer every now and again because adding a 2nd room gets to be very expensive

, we stay in hotels). This does not include semi-local overnight trips to visit family.
Our family is known for pretty great vacations though. We are an ‘excursion’ heavy family, so most of our vacations are fun places with great excursions rather than staying at an air bnb for a beach week (just our preference).
I know that it’s not a requirement to take them with you, but we truly look at our Au pairs as members of our family, and it seems extremely rude to not give them the option to join us. If my 20 something niece or cousin lived with us, I would always offer her the option to join us on vacation, so it seems odd / rude that I would not extend that same opportunity for our Au pairs.
The Au pairs have always been helpful during the vacation (helping on flights, covering a date night, getting up with the kids one morning during the vacation so that we can sleep in), but the family vacations are also never counted as part of their vacation weeks.