Some would be worked to death and the rest would be killed in the implementation of the Final Solution to the Jewish Question.[328] Initially the victims were killed by Einsatzgruppen firing squads, then by stationary gas chambers or by gas vans, but these methods proved impractical for an operation of this scale.[329][330] By 1942 extermination camps equipped with gas chambers were established at Auschwitz, Chełmno, Sobibor, Treblinka, and elsewhere.[331] The total number of Jews murdered is estimated at 5.5 to six million,[239] including over a million children.[332]