“Mrs. Sendler […] smuggled 2,500 children out of the Warsaw Ghetto during the last three months before its liquidation. She found a home for each child. […] Mrs. Sendler listed the name and new identity of every rescued child on thin cigarette papers or tissue paper. She hid the list in glass jars and buried them under an apple tree in her friend’s backyard. Her hope was to reunite the children with their families after the war. Indeed, though most of their parents perished in the Warsaw Ghetto or in Treblinka, those children who had surviving relatives were returned to them after the war.” (source; also see this site)