The book could also be sold elsewhere to earn money to help free illegally detained prisoners. Maybe a One for One program could connect a specific child with a book buyer. The person who buys the book could be paying for a book to be produced for the child, as well as helping support a campaign for that child's lost family member. Besides helping to support the movement, this would also raise awareness about the issue.
At the workshops, the children begin by exploring their personal experiences through art and writing. Then, they all come together to create a fictional story that expresses their fears and feelings around the loss of their family member. Each child could illustrate a page of the book. Consistency in illustrations could be achieved by limiting the materials that children work with by color, medium, etc.
This could take place in mobile units as well, as suggested by Anne-Laure and Yen.