My grandfather was a doctor during WWII, and his son (my father) was born during the war. At that time, soldiers in the trenches kept getting infections under their foreskins because they had no way to wash themselves regularly enough there.
issues of unwashed foreskins in trench conditions
This is a common myth, but completely ridiculous. Foreskins don't get infected simply because of going several days without washing them. Why was the United States supposedly the only country with this "problem"?
The real situation was that plenty of soldiers were visiting prostitutes (and if they had the time for whores, they had time to wash) and getting venereal diseases. It was popularly believed that circumcision would reduce the uptake of such infections, and so many medics liberally circumcised; but in fact it had no real effect on future STD rates. Quite a few guys came home circumcised, and instead of telling their wives and girlfriends that they had gotten circumcised because of VD, they said that war conditions necessitated it. Which is bollocks.
The stories go on and on: it was because of sand and desert conditions. It was because of jungle conditions. It was because of trench warfare. It was because of extreme heat. It was because of extreme cold. None of them really make any sense, and in any case it would have been tactical suicide to take so many men out of combat for surgery and recuperation. The circumcisions were done in downtime, around times of R&R, shore leave and brothel visits.
As for post-war, I doubt that combat conditions was much on the mind of anyone when babies were born. Medical insurance was booming as a job benefit in peacetime and birth was moving rapidly from the house or farm to the hospital (worth noting that most births today in the Netherlands are back at home again). This medicalization and standardization led to "assembly line" thinking and boys were cut as a matter of course. In many or most cases, doctors and nurses didn't even bother obtaining consent; circumcision was as routine as a heel stick. This didn't begin to change in earnest until the 1970s.
It's cool that your family evolved out of the idea that circumcision was necessary or desirable, and that you and your brother benefited.
(BTW, I have never in my life heard WWII referred to as "the war to end all wars" or even "the war to end war".)