Au pair programs and visa information in United States of America:
People from almost all countries can become au pairs in the United States. However, in order to legally become an au pair in the US it is necessary for an individual to obtain a J1 Visa. In order to get a J1 visa an au pair has to go through one of the US government designated au pair agencies. With this visa, au pairs may work for a family as an au pair for 12 months and may apply to stay for an extra month in order to travel round the US. However, after that time the au pair is expected to return to their home country. Also, in order to work as an au pair in the US, an au pair must produce a certificate of health, a certificate of good conduct and experience in the field of child care.
LINK: Designated Sponsor Organisations for the J-1 Visa Program for au pair placements
For more information on being an au pair in the US the US Department of State offers some information on the au pair programme in the USA online.