Obligation to apply through Au pair agency
You can only participate in the program “stagiaire aide familial étranger” if you stay for a minimum of 3 and a maximum of 12 months. The maximum period it can be extended to is 18 months in some of the country.
In some country the duration of the au pair stay should not exceed one year.
Some of the county visa allows a 2 year stay, but cannot be extended.