The basic problem is that societies have been geared up for having a lot of kids, based on the reality throughout history until very recently that most kids died before being able to breed. But advances in medical care, hygene, etc. have cut that throughout most of the world dramatically. The required solution is to cut birth rates accordingly, and thus we have seen the Chinese "one child" policy, and similar things throughout the developing world.
But what has to be remembered is that much of the movement towards much smaller familes comes from the women. They are the ones who don't want to spend their lives making babies, and then slaving over raising large families. And, don't forget, living in poverty. The best way out of poverty is to limit famility size. A lot.
Until very recently, the women in Moslem countries were kept barefoot, ignorant, and pregnant. Much more ignorant than the men, and this was working to keep the birth rates high. But even without getting formal education, many women now have access to satellite TV, the Internet, etc., and are finding out about the rest of the world, that the rest of the women in the world don't live that way, that there are really good reasons not to, and that there are ways to avoid it. And, that is slowly going to kill Islamic terrorism.
But, as was pointed out by one of the most dangerous economists of the 20th Century, in the long run, we are all dead anyway.