Au pair programs and visa information in Netherlands:
In order to work as an au pair in the Netherlands, there are various requirements that an au pair has to meet. These include an au pair having health insurance with coverage in the Netherlands, undergoing a tuberculosis test in the Netherlands and not previously having stayed in the Netherlands on a residence permit.
If you meet these requirements, in order to work in the Netherlands, you are required to get an authorisation for temporary stay, an MVV. There are two ways in which you can apply for an MVV. An application can be made at the Dutch embassy, in your country of origin. The embassy will then send your forms to the IND in the Netherlands and, if your application is approved by the IND, the embassy will issue you an MVV. Alternatively, your host family can send a "Request for advice on an authorisation for temporary stay" directly to the IND. If the IND issues a positive advice you can then apply for an MVV at the Dutch Embassy or Consulate in your country of origin.
Once you have received an MVV, you may go to the Netherlands to work. Once you enter the Netherlands you are required to report to the Aliens police within 3 working days. If you are planning to work in the Netherlands for longer then 3 months, you are also required to apply for a temporary residence permit.
Au pairs from the Member States of the EU do not need an MVV or a residence permit to work in the Netherlands. However, whilst a residence permit is not required for EU nationals, the Dutch Government suggest that it may be useful to get one anyway as other authorities may request it. For example, it can be used to open a bank account in the Netherlands. Au pairs from Australia, Canada, Iceland, Japan, Monaco, New Zealand, Norway, Switzerland and the US do not require an MVV to work but they do need to apply for a residence permit once they have arrived in the Netherlands.
(For a full list of the requirements for both you and your host family and for more information on the visas required see the visa information on the Dutch Government site.)