Jewish Family Pretends To Be Polish to Escape Holocaust

I read this book back in 2005, I’m not sure when it was written but I’d assume at least 10 years prior to when I read it.

All I remember about the cover of the book is that it’s background was purple and the lettering was yellow/gold.

I remember that the family was a Jewish family and they were pretending to be Polish in hopes that it would help them escape the Holocaust.

I specifically remember a part about them being on a train and the mom and daughter were separated from the dad and son.

When they were separated on the train one of the conductors or nazi officers gave the mom and daughter an exam, I vaguely remember it resembling assault?

I also remember that the daughter spoke Polish and that she used to talk to the officers so that they wouldn’t know her and the family were Jewish.

That’s all I remember, if anyone knows please please let me know! I have been searching for this books for 5 years now.

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>1 amandalynnex3: Number The Stars by Lois Lowry maybe