Children were especially vulnerable in the era of the Holocaust. The Germans and their collaborators killed as many as 1.5 million children, including over a million Jewish children and tens of thousands of Romani (Gypsy) children, German children with physical and mental disabilities living in institutions, Polish children, and children residing in the occupied Soviet Union. In the ghettos, Jewish children died from starvation and exposure as well as lack of adequate clothing and shelter. Because children were generally too young to be deployed at forced labor, German authorities generally selected them, along with the elderly, ill, and disabled, for the first deportations to killing centers, or as the first victims led to mass graves to be shot. Upon arrival at Auschwitz-Birkenau and other killing centers, the camp authorities sent the majority of children directly to the gas chambers. In concentration camps, SS physicians and medical researchers used many children, including twins, for medical experiments that often resulted in the deaths of the children.
Between 1938 and 1940, the Kindertransport (Children's Transport) was the informal name of a rescue effort which brought thousands of refugee Jewish children (without their parents) to safety in Great Britain from Nazi Germany and German-occupied territories. Across Europe, some non-Jews hid Jewish children and sometimes, as in the case of Anne Frank, hid other family members as well. After the surrender of Nazi Germany in May 1945, ending World War II, refugees and displaced persons searched throughout Europe for missing children. Thousands of orphaned children were in displaced persons camps.