How did war impact Jan?

Jan is a street child orphaned in the war. He is quite wild and almost feral as a result of taking care of himself on the streets of Warsaw. He is talented at all the things that are illegal, such as fighting and pickpocketing. Jan is very combative; he hates Germans and soldiers, so it is possible that he saw his family taken away by the German military. He is oddly sentimental about seemingly worthless things, such as three dead fleas given to him by an escaped chimpanzee. It is this love of acquiring and hoarding in his little wooden box that ultimately brings him together with the Balicki children and their quest to find their parents: Ruth recognizes the silver sword in his box from her house. Jan is not much of a people person, but he has a special bond with animals, all of whom love him, and with Ruth.

I personally agree with Jill D. I think some would consider Jan a troubled child or a criminal when really I think that he had been through a lot and it made him who he was. Since there was no backstory for Jan, I like to think that he witnessed his family being taken away from him by the German soldiers and that is why he hates them as much as he does. And maybe they had a pet and all of his family was taken away from him but the German soldiers left the pet and that is why he had such a strong bond and connection with animals no matter what species it was. I haven't thought of why he could be so attached to the fleas from the chimpanzee but maybe somebody else has a theory for it.