I just had to search for the verses:

Like arrows in the hand of a warrior, so are children born in one’s youth. Blessed is the man whose quiver is full of them. He will not be put to shame when he confronts the enemies at the gate Psalm 127:4,5.

I think there was a fear when the Irish invaded America that they would fill the land with papists but I think it's fair to say it never happened. I don't think Muslims (fingers crossed) will fill the land with little Mohammads either. With a bit of luck, they'll be too busy chasing the mighty dollar to live a fundamental life.

They also regularly lose their offspring to the faith in various ways, as the Real World has a nasty habit of intruding on their ideals. Authoritarian religion isn't a sustainable phenomenon, and in fact, I believe it's in its death throes. The only open question is how much society may regress, possibly even into some dystopian detour. However ... in the long game, they're finished.

I predict that fundamentalism will be a crackpot fringe a hundred years from now, and religion generally in a thousand years.

Patience and courage.