However, how true is it that an entire generation of French males were lost in WWI, and the only way to repopulate the country was to have "love children" sans marriage?
Wars in general, and World War I in particular, are not usually demographic disasters. That's because wars typically only kill men, and men, from a demographic perspective, aren't really that important. Famines and epidemics have much more profound demographic consequences, because they kill women and children. The Spanish Influenza outbreak and the famines experienced in Russia during its civil war, therefore, were much more important in terms of effects on population growth. Only very unusual wars, such as the War of the Triple Alliance
, have disastrous demographic effects.
As for the French in WWI, they were well aware that they were losing the demographic battle with Germany, and had been for many years. The French army, consequently, had a liberal leave policy for soldiers, who were strongly encouraged to go back home and get reacquainted with their wives and/or girlfriends. The French term for "leave" is "permission
," and soldiers soon started calling it "spermission
" (yes, the pun works the same in English).
The French demographic growth rate was already quite low before the outbreak of the First World War -- close to ZPG. There was a population dip after the war, but by 1931 France was back above pre-war population levels. So there was no need for the French to repopulate the country with "love children."