While it is up for debate as to whether or not the Children's Crusade actually happened or not, that doesn't change the fact that the account has famously gone down in history. What we also don't know is exactly what about the Children's Crusade Amanda's book focused on. It could be a children's book that gave Maniac a grandiose version of events, or the book could be a much more analytical examination of the actual historical records. Either way, readers are told that Maniac was fascinated by the book, and he kept it for multiple days in order to read it multiple times.

It's entirely up to individual readers to think of reasons why the author chose that particular book and topic for Maniac to read. I think that the reader has solid grounds to focus on the fact that the Children's Crusade was a movement started by children and carried out by children. The fact that it failed is less important for Maniac in my opinion. The Crusade shows Maniac that children can be powerful, and children can fight against something that they believe is morally and socially wrong. The Crusade was religiously focused, but Maniac's fight will become a fight that is racially focused. He doesn't lead an army against adults or anything like that, but he shows a community of people that skin color is irrelevant.