Other people will give you far more information than I can but there is a big difference between a nanny and au pair. If you are an au pair then you are limited in the hours you work and you normally live with the family. I believe the family should pay your health insurance and for a language course. Also I don't think you are allowed to be the same nationality as the family.

As a nanny you would be paid a much higher salary but I don't think the family pay your health insurance and there is no requirement for the language course.

In short what this family are arranging does not sound right.