Help - can you identify this book?

[mummytime]

It isn't "The Silver Sword" although I thought it might be.

I first read it when I wanted to re-read "The Silver Sword" but it was a different story, and now reading "The Silver Sword" to my DD I am very confused.
It also isn't "I am David"

Its World War II. There is a boy in Warsaw. He's left behind or some other way separate from his family. There is a bit where he is in the Warsaw Ghetto (which is how I know I haven't totally imagined it, as this was the first time I'd heard about that).
He may end up in a Prison Camp, or being transported somewhere.
But he escapes - somehow. He then travels across Europe to Spain (maybe heading to Portgual?).
I think he has something with him, maybe a broach or badge that helps him be identified at the end.

Is it this one?

www.goodreads.com/book/show/1120973.Child_of_the_Warsaw_Ghetto

I wonder if it's one of Christa Laird's books, Shadow of the Wall and Beyond the Wall about a boy who lives for a time in Janus Korczak's orphanage, but escapes from Warsaw and joins the partisans, thereby escaping getting transported to Treblinka with the rest of the orphans. From what I remember there's nothing about a prison camp, but the brooch or badge rings a bell - he rescues his baby sister by smuggling her out of the ghetto and Beyond the Wall is written as flashbacks from 1970s New York where the boy now lives, and his search for his sister. DD2 was fascinated by these books, and they spurred her on to find out all about Janus Korczak's life and work. An amazing man. It's some time ago now, so I'm vague on details.

It's not one of the Henderson Boy series? They're fairly recent, so sounds unlikely. But I know in one, one of the main characters has been left behind in Nazi Germany and has to make his way across Europe on his own as the others believe he is dead. I haven't read them, but dd1 was very keen on them for a while.