The au pair is considered as a full member of the family during the temporary period of the au pair stay. As such, he or she helps the family with childcare and can be asked to assume some light household tasks. In return, the host family provides free board and lodging, as well as pocket money. However, the au pair is neither a housekeeper, nor a nanny.
The main purpose of the au pair placement is a cultural exchange, which gives the the au pair an opportunity to improve his or her language skills. For this reason child minding in your own country doesn't count as an au pair stay. The au pair should also attend a language course in the host country. He or she should, however, have some basic language skills beforehand. Whether it is the au pair or the host family who pays for the language course depends on the prevailing practice of the relevant host country. The same applies to the cost of travel and insurance.