Short answers, pulled from the story.
Around 6 million Polish citizens perished during World War II, roughly one fifth of Poland's entire prewar population. The most authoritative modern estimate, published by the Polish Institute of National Remembrance in 2009, puts the total at between 5.6 and 5.8 million ethnic Poles and Polish Jews, with an additional 150,000 deaths attributed to Soviet repression.
Approximately 2.7 to 2.9 million Polish Jews were killed in the Holocaust, according to the Polish Institute of National Remembrance's 2009 study. Polish researchers estimate that 1,860,000 Polish Jews were murdered in the Nazi death camps, with the remainder dying in Jewish ghettos, aboard Holocaust trains, and in mass shooting operations.
The estimates differ because the 1947 Polish government report was compiled under political pressure by a communist-dominated government and used incomplete data. Soviet control of Poland suppressed independent scholarship for 50 years after the war, and the changing borders and ethnic composition of Poland made population accounting difficult. Scholars also disagree on how to classify ethnic minorities including Ukrainians, Belarusians, and Polish-speaking Jews.
The Katyn massacre was the Soviet murder of 22,000 Polish military officers and government officials during the occupation of eastern Poland. The Polish Institute of National Remembrance includes it in the confirmed death toll of 150,000 Poles killed under Soviet occupation between 1939 and 1945.
A source cited by the Institute of National Remembrance put the number of children kidnapped from Poland at 200,000. Only 30,000 of them were eventually returned to Poland after the war; the others remained in postwar Germany. The kidnappings were part of Generalplan Ost, which aimed to Germanize children deemed to have purportedly Aryan traits.
The Institute of National Remembrance estimates that 1,897,000 Polish citizens were taken to Germany as forced laborers under inhuman conditions between 1939 and 1945. The historian Czeslaw Luczak put the number higher, at 2,826,500. Polish laborers were forced to wear identifying tags marked with a letter P, subjected to curfews, and confined to segregated barracks.