Immigrant group birthrates go down to the native level usually after only one generation. In the Netherlands, the 2013 birth rate was just 1/3 of that of 2003. It's a little more then natives, but quickly diminishing. We had like 16.000 refugees in 2016, not all of whom are muslim, not all of whom will be permitted to stay, and not all of whom will stay in the Netherlands at all. And then I don't even include secularization.
But hey, whatever.