The veneer of historical reality is thin on the baldly nativist and manipulative Serbian World War II movie “Dara of Jasenovac,” a slickly made extermination camp drama about child peril that will test the patience of even the most rigorous students of cultural representations of genocide. Fascist Croatia under the terror-driven Ustase government was indeed a nightmarish puppet regime of the Axis powers, and its massive Jasenovac complex of camps was one more hell on Earth for Jews. But what director Peter Antonijević’s epic of barbarism and sentimentality wants to drive home is that the annihilation of ethnic Serbs was the real focus, and that children got their own camp. If only it didn’t smack of scoring points in a longstanding regional feud. When there’s a scene in which the visiting Nazi bristles at the display of one-on-one sadism toward Serbian prisoners from his crisply uniformed Croatian hosts (which include incestuous brother and sister officers), you know you’re in agenda territory.