The primary differences between a nanny and an au pair are as follows:
An au pair must meet specific criteria to participate in a government-sponsored Au Pair Program. In the United States, au pairs must be between the ages of 18-26 with demonstrable childcare experience, who come to the U.S. to stay with a family for a cultural exchange experience for one year. Au pairs typically don't make a career out of childcare work as nannies more often do.
Many families and au pairs participate in government authorized au pair exchange programs where there are defined rules and requirements. See Family Requirements or Au Pair Requirements for more information. The relationship between a nanny and family is that of employer and employee, not governed by an exchange program, rather, governed by contractual law.
Nannies may be older and more mature than some au pairs, with several years of live-in childcare experience. Nannies are not necessarily seeking a cultural exchange, rather, it is the long-term career-building experience in child care they are seeking.
For detailed information on how much to pay your au pair or nanny, please see Au Pair & Nanny Salary
The pay for international au pairs working in the U.S. must be a minimum of $195.75 per week, based on the FLSA. Domestic nanny salaries may be higher: $300 up to $800 per week depending on your location, the candidate's experience, and additional responsibilities: cooking, cleaning, household management, etc. It is not required to pay employee taxes for your international au pair while she/he is participating in a qualified J-1 Au Pair Program in the United States, where it is required that employment taxes be paid for a nanny.
Foreign au pairs seeking to enter the United States may be eligible for a J-1 au pair visa, valid for one year, and extendable for a second year, that is allowed by the US Secretary of State, through a sponsoring J-1 Au Pair Agency. Foreign childcare providers outside of the age range of 18-26 do not qualify for the U.S. Au Pair Program but may qualify as a nanny, regardless of age in another country. For more information on age restrictions, click here: Au Pair and Nanny Age Requirements