References are letters of recommendation. They provide information about a person's performance, social skills, personal attitude and capabilities. Therefore, you should ask for references if you wish to get a better idea of your favourite au pair or host family.
You may, for instance, ask your au pair's previous or present host family if they would be willing to provide a reference for the au pair. The au pair's teachers, former or current employers, or families who employed your au pair as a babysitter, may also provide information. To enquire about a host family, an au pair may contact former au pairs of the family, the teachers of the host family's children or the host parents' employers.
References may be provided in written form. However, it is also possible to directly speak with the persons who provide these references, should they agree to do so.
In addition to references, host families in particular, can ask their au pairs to provide a health or police clearance certificate. In some countries, au pairs need to submit their health certificate with their visa application.