To invite an au pair means to have someone else living in the same house. And to live together with others means to treat each other with respect. A part of that is to accept that everybody needs their private space and time for themselves.
If a host family invites an au pair to live with them for a while, they let a stranger come to their house and both have to get used to live with one another. The familiy sets a schedule together with the au pair, so it’s clear when the au pair is supposed to work and when they have their time off. For many host families there is always the question, if and how many rules they can give the au pair. One of those would be a certain time, the family expects the au pair to be back home. But is a family allowed to give a curfew?
Be strict but accept that the au pair is an adult
If the au pair has to work the next day, the host family can absolutely give her or him a curfew. That way they make sure, that the au pair will be awake in the morning to get the kids ready for school. The host family should expect a level of responsibility of the au pair and be sure that even without a curfew the au pair wouldn’t stay out the whole night on a work night. But you never know, so a reasonable curfew can be set. To be home at 10 pm might be something for highschool students. If an au pair should be home at 11 pm or midnight, that would sound fair.
If it’s not a work night though and it’s the au pair’s day off the next day, there should not be a curfew. The au pair should not come home totally drunk and make a lot of noise, but be considerate of course, yet the host family shouldn’t forget that the au pair is an adult that can go out and have a good time and come home at 4 am in the morning, if they like to and if they don’t have to work the next day.
In case of a curfew, it should be written down in the contract between host family and au pair.