Hi there, I have never take our nanny on hols with us but I'm interested in stories of those who have!
Nannynick has covered a lot..and I'd definitely agree, don't think of it as a holiday or a 'bonus' (unless you're getting tonnes of free time).
I'd guess the sort of accommodation will govern a lot of the questions I'd want answers to.. if it's a house or a villa, house, it could be a home from home, if it's holiday apartments or a hotel, it could be harder... If it is a hotel / holiday apartment, I'd add:
meals - will you all eat as a 'family' or will you feed the children then sit in a room with them whilst the parents go out?
Is there any separate space for you to (escape!) switch off / have down time?
swimming - will you supervise the children in/around a pool etc, if so are you a swimmer?
Also look at transport. If you're in the middle of nowhere, will you need a hire car or similar?
On the plus side, it could be a great opportunity to travel a bit and learn / extend a new language though..