Final answer:
The common theme in the provided texts is the hardship of family separation and the yearning for reunion, often in the context of migration.
Step-by-step explanation:
The concept common to the texts provided is that they all convey the profound impact of separation from family and the deep longing to be reunited. Both the passage about Enrique from 'Enrique’s Journey' by Sonia Nazario and the other narratives involve individuals who are distanced from their loved ones, often due to migration or external circumstances beyond their control. While not all texts specifically mention children traveling alone to reunite with parents, they do reflect on the broader themes of family separation and the universal desire for connection and the safety of loved ones.