Being an orphan
Being an orphan is a vital part of Felix's identity. When he was six years old in 1939, Felix's parents dropped him off at a Catholic orphanage so that he would be safe from Nazi aggression and death. Felix has spent most of his life as an orphan, without parents to love and guide him. Felix thinks that his parents are alive; readers know that the Nazis killed his parents and were victims of the Holocaust. Being an orphan has radically changed Felix's life and caused him tremendous hardship and despair (including having no food and being in difficult situations he otherwise wouldn't have been in), showing how transformative an effect abandonment can have on a child.
Genocide
Once is set during the Holocaust, one of the deadliest genocides in history. The Holocaust was masterminded and perpetrated by Adolf Hitler and his Nazi party and was responsible for the deaths of over seven million people—predominantly Jewish. Because of his age, Felix could not completely understand what was happening around him. Still, Felix understood for much of the novel that the people who called themselves Nazis didn't care for Jewish people and did violent things to show it. For instance, Felix saw people riding to death camps, saw executions, and witnessed the Nazis doing other awful things so that they could carry out their genocide. Through this theme, Gleitzman illuminates how radically genocide can alter the fabric of a country and the people that live within it.
Racism
The Nazi party is synonymous with racism. From the time they took power, the Nazi party advanced racist ideology. Felix witnessed the effects of that racist ideology on himself and those around them. Perhaps most significantly, Felix saw how racist ideology influenced the Nazi's decision to murder an entire race of people. He also saw how racism influenced the Nazi party's decision to destroy books they found unworthy around the country. Despite going through things that no one should have to go through, Felix came out of his experiences with a new understanding of how damaging racist ideology can be. Racist ideology can take hold in a country, influencing them to do horrible things. Through this, readers see how important it is to avoid allowing politicians and racist political parties to take power. If they do, it can have disastrous consequences.
