Bedrich Fritta was a Jewish Czech artist forced to produce construction plans and diagrams for the Nazis. His son Tomas was one when the family was sent to the Theresienstadt ghetto. Bedrich made unauthorized drawings, too, documenting and criticizing the horrific conditions in the Nazis' model concentration camp. And he secretly created a picture book, To Tommy, For His Third Birthday, Terezin, 22 Jan 1944, full of happy, hopeful images to spur his son's imagination and to survive the privations of their current situation.
Some of Bedrich's unofficial drawings were discovered, and he was sent to Auschwitz, where he died. His wife died in Theresienstadt. Tommy, an orphan, was discovered in prison by a family friend, who adopted him, and helped recover the book, which had been hidden in the wall of Bedrich's ghetto office.
Fritta's book has been published in a couple of formats. In 2000, the noted Czech writer Ivan Klima, who was slightly older than Tommy, and who had also been in Terezin, published a short story that used Bedrich's Tommy illustrations. That book, This is not a fairy tale -- it's real!, is available at the Jewish Museum in Prague.
I've seen cover images of both German and Dutch editions of To Tommy from 1977 and 1980, respectively. But the trilingual edition [CZ/EN/HE] published by Yad Vashem in 1999 seems to be the best option.
The BBC reports To Tommy will be used by Yad Vashem to help teach the Shoah to young children in Israeli schools.
Jewish Museum Berlin exhibit of Fritta's artwork: To Tommy, for His Third Birthday [jmberlin.de]
A Holocaust book for young children [bbc]
Buy a copy of To Tommy, For His Third Birthday, Terezin, 22 Jan 1944 on Amazon [amazon]