Do you have a link to that statistic about the Netherlands? I did a Google search and found one site called "jihad watch" which had some of "dhimmi" index, which I don't consider too reliable. The Netherlands itself reports that there are 1 million Muslims in that country, 5.8% of the population.
I would be shocked if 5.8% of the population were capable of producing 50+% of births, no matter how much the Dutch seem to have given up on procreating. Certainly if the Muslim community is having that many children, a good share of that 6% wouldn't even be old enough to have children themselves!
I remember hearing that a majority of kids born in Rotterdam were Muslim; perhaps that's what you meant.
Well, in the case of France, it's not that hard to figure out.
When you consider that Moslems are 10% of the population - and that they're younger, with a TFR of five or six children per woman versus one for native French.
I did a MetaCrawler search (I don't Google), and a Newsweek article says that "in a decade or two" a majority of Dutch newborns will be Muslim, so I guess I was misinformed about the current percentage of Muslim babies in the Netherlands; maybe I read about the Rotterdam stat and got confused. Here's the Newsweek article: http://msnbc.msn.com/id/3540615/
If a majority of Dutch babies by, say, 2020, are Muslim, and heavy Muslim immigration continues for a few years after that, wouldn't the Netherlands have a Muslim majority by 2040?
BTW, a factor that would simultaneously reduce the number of non-Muslim Dutch while decreasing the necessity for larger numbers of Muslim immigrants is the Dutch euthanasia law that has started to be used in cases in which the old or sick person has not necessarily consented to be euthanized. Who knows which way euthanasia will cut in the demographic battle for the Netherlands, or if France will adopt a similar policy.