That probably explains it.
Not my area, but it's my recollection that they would have been considered to have dual citizenship since they were born of Polish parents. The mother probably did have a window in which she could have appealed to American diplomats to help get the children out, but she probably would have had to travel to Berlin (or at least a city with counsulor offices) to make the appeal, and probably couldn't do so.
My grandmother had to save money to get my dad's younger brother out. How she got the money I have no idea. They sailed home on the Ernie Pyle.
What a time it must have been.