When a SS General’s daughter falls in love with a Jewish boy in a concentration camp, they must stand out together to get back his family and help the Jews escape from the Germans.

Good start and good end. The middle needs more clarification though and was a bit too clunky to read smoothly. Perhaps using the buzzword of Nazi could enhance the engagement of introducing the protagonist. Here is an example:

When the daughter of a Nazi general falls in love ...

Also, should the 'falling in love' become precipitated by a major event? Falling in love is not a single moment but rather a developmental process. Perhaps your logline could include the protagonist MEETING the Jewish boy - this event leading to their falling in love. This would read and function better perhaps than presenting a developmental process as a life changing major event.

Also, the action should remain focused on our protagonist. Sure the Jewish boy is struggling against the threat of being killed, but the focused threat is not this, it is the high stakes of the daughter rebelling against her father's subscription to genocide that generates appeal and drama for this plot. So maybe use 'she' instead of 'they' before must. It's a minor but important alteration.

Additionally, the closing action of your logline could be further enriched by what I've discussed in the previous paragraph. Perhaps the action is:

She must rebel against her father, assisting her lover and his family escape the train bound for Auschwitz.

Introducing an element a little more specific than simply helping them escape -- like attempting to get them off a train -- adds to the tension and stakes which you've already done a great job with when you established the primary character conflict of familial divide.So I love your concept, but perhaps something along these lines could achieve greater impact and engagement to your story.

When the daughter of a Nazi general falls in love with a Jew, she must rebel against her father to assist her lover and his family escape the train bound for Auschwitz.

Why not go full throttle and switch from daughter to wife. Because of Who she was married to, she can manipulate the soldier within the camp.

When the unhappy wife of the warden of a SS Concentration camp recognises one of the inmate as her former fianc?, she decides to help him and his Jewish family escape.

you could create the initial tension by revealing that he decided against marrying her on the order of his family because she was not Jewish. Initially by revenge, she saves his life by forcing him being her servant. Then their relationship rekindles. But the husband is soon back and reveal that all prisoners will be gassed. That's when the dilemma occurs.

You could also turn that into some kind of sadomasochistic relationship, with her now firmly in charge. That remind of an old movie?The night porter. A movie not to everybody 's taste.

Agreed with DPG.

It would also have to be made clear that the girl has the means with which to save the boy and his family. Oscar Schindler had his vast fortune and influence at his disposal, but what doe the girl in this story have? How will she actually go about saving the boy?

Perhaps up the age group to teenagers instead of children, this way she could arguably manipulate the system.