One main theme is probably resilience. Orphans often have to be very tough to survive. Another could be hope, as they hope for a better life. And also loneliness, as they are without their families.
The main themes in 'The Orphan Based on a True Story' would include the struggle for belonging. Orphans are without a family unit which is so fundamental in society. Also, the theme of loss is evident, not just the loss of their parents but also the loss of a normal childhood. There may also be a theme of kindness, as some characters in the story might show kindness to the orphan in their journey.
The themes are likely to be complex. There's the theme of identity, as orphans may not know their family history or who they really are. The theme of survival in a harsh world is also important. They have to find ways to get food, shelter, and education. And there's the overarching theme of the human spirit, whether they can rise above their difficult circumstances or be crushed by them.