You can say about the age of the kids, that you are experienced with, or that you like to live in a small town nearby the nature or you can say that they seems to be an active family. I am an active person that why I am looking for an active family so I will get a chance to do or trying different things. Or you heard that Denmark is a nice country with happy people. Very safe and equal. You fancy Europe in general and love to learn another foreign language or practice your English. They are also particularly looking for an Au Pair from Thailand. Or there are many au pairs live in the near neighborhood.