Hello pilar0194, and welcome to ScamWarners.
Those messages show no typical signs of being a scam, and they are written in a style consistent with a Dutch family. Of course, you will still want to be sure never to send money to a host family, nor to anyone who they put you in contact with; but I think that, with that precaution, you can proceed to a telephone conversation, and getting to know more about the family.
You can read an overview of the requirements for becoming an au pair in the Netherlands here:
http://www.aupair-world.net/index.php/a ... ds/au_pairYou were correct to include all details, because this helps us identify whether or not messages are from a scammer, but as this family are not showing any signs of a scam, I will now remove their details, for their privacy.