Whether peculiar or not, growing up during the mass carnage that was World War II was extremely difficult, and children like Grandpa Portman faced extreme challenges. If they were like common children, the peculiar children in Miss Peregrine's house would have been evacuated from their family homes when the war started and sent elsewhere to keep them safe. Either parents were afraid to keep them in an area targeted for air raids, or the children were Jewish.
Children in the United Kingdom were particularly affected because of the frequency of enemy attacks on UK soil. Children accounted for one in ten of the deaths in the London Blitz from 1940 to 1941. Evacuation of children from cities like London out to the countryside became widespread through an arrangement called Operation Pied Piper. This operation attempted to remove 3.5 million children in three days from the six cities that were deemed most vulnerable to German attack. In the end, the operation was able to evacuate 1.9 million children from these major cities. Children who stayed at home or returned home before the war's end were subject to much of its harsh realities on the home front, such as food rationing.
In those areas of Central Europe under Nazi control, many children suffered a far worse fate. It is estimated that the Germans and associated Nazi sympathizers killed up to 1.5 million children over the course of the Holocaust. Jewish children, Romani (gypsy) children, and physically and mentally disabled children were all targets, killed due to what the Nazis called a "preventative measure." Had Grandpa Portman not been sent from Poland to Wales, he likely would have been taken away due to his family's Jewish beliefs.