I'm surprised to read that. Here in the UK, having a live-in au pair doesn't excuse you from paying the minimum wage for all the hours that they're working (approx $2300/month for a 35 hour week). You can deduct an amount to account for the fact that you're providing accomodation but it's strictly limited (approx $400/month).
From what I can see online, the average compensation that an au-pair in The Netherlands receives is 300 euro per month, with living expenses being covered by the family. There is no minimum wage requirement for au-pairs like in the UK or the US.
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The Netherlands has a weird and exploitative setup where you can classify your au pair as a "cultural exchange", and then pay them literal peanuts (room and board plus a token amount of "pocket money")