This is a significant assignment, because the events in Refugee are so rich and complex. As a young adult novel, almost all the issues in it could be viewed through the lens of relevance to youth. I have some suggestions below that hopefully can help you fill out a mind map.
Family—the idea of family staying together and safe is a central idea for all three main characters. This is something every young person can connect with, as family is so central to their lives. When the risks of staying put are greater than the dangers facing an uncertain move, that is when families decide to become refugees. Their hope and commitment to staying together is what pulls them to make such a risky decision.
Survival—you could argue that this is not simply an issue for youth, but it has a strong pull for a young person, with so much to live for and so many dreams for the future. What would you not risk, if it meant the chance to grow up and pursue your dreams? Surviving the treacherous journeys across the water is not a guarantee. These young refugees are confronted many times by the possibility that, in fact, they may not live another day. That, too, pushes them to prioritize survival above all else.
Justice—young people have a strong concern for justice and doing what is right. In the novel, the reader is also confronted with this idea. Some of these refugees are escaping to countries that do not welcome them. Is that right? What does fairness mean, when it comes to situations like these? The hope is that, when reading Refugee, a young person might come to understand a bit better the plight of people fleeing these kinds of dangers. Justice is a central idea and a universal one.