first of all, the children are recruited into the HJ group and they go through this propaganda programme where they are brainwashed in a nationalistic fervour that they simply are the best, and that the Nazi Party is there to help everyone. Part of the responsiblities of the HJ was to clean the streets, plant plants, involve in sports, collect charities for Winterhilfe of the soldiers on the fronts, etc... They are told that they will become the Elite German Army, and hidden from the frank truths of the evils of the Nazi Party. Some of them are told that Jews are sent to other countries, or outside of Germany. Not all of them know that the Jews and other prisoners are killed.
They are told that whoever defects against the Nazi Party have to be sent to Worker's Camp to be "rehabilated" and to come back to the society as a proper Nazi supporter. For this reason, children are ordered to listen as spies to their families at their homes, and to report any dissent comments against Hitler and the Nazi Party. Then the child believes that their family member can be sent to camp to "relearn" about the wonderful things about the Nazi Party. Little do they realise that their actions were quite adverse to their family members.
Swing Kids was one of the resistance groups during Nazi time. Like I said in my first posting, even resistance groups' members were forced to either serve in the Wehrmacht (army) or the HJ (Hitler's Youth).
The Nazi Government does not work the way you (Angel) said, "what if the govt told teenager boy to murder his sister." They would collect evidence, then find a charge against the sister. For example, if the sister involved with a group who printed flyers denouncing the Nazi Government, the govt would tell the brother that the sister is a traitor to the Nazi Government. The brother, who might feel a big responsibility to the government and country, probably would agree with the govt and turn her into the govt to be imprisoned and rehabilated.