How did the image of the child from the Unseco publication inspire Serraillier?

This is the only quote regarding Unesco publications that I find in the book;

Unesco publications with titles like ‘Children of Europe’, and ‘War-Handicapped Children’ also helped. Ruth, Edek, Jan and Bronia were based on real children in Red Cross records. But in real life, they all came from different families. The real ‘Edek’ died of his TB.