Final answer:
The Lost Boys experienced significant changes, including a shift from naivety to a maturity driven by the need to survive and protect what is dear to them. This maturity is shown in their response to conflict and adaptation to challenging circumstances, moving away from idleness to a state of alertness and fierce vigor.
Step-by-step explanation:
The biggest changes that occurred in the Lost Boys seem to revolve around personal growth and shifts in perspectives due to their experiences and challenges. The passage suggests that the characters have grown to fight for their very survival and everything that is meaningful to them, including their homes, food, family, and future. This indicates a significant transformation from a more naive understanding of life to one that is marked by hardship and resilience. Moreover, a strong theme in the change seems to be the development of maturity, especially when dealing with conflicts, as shown in the scenario with Andy and Lucas. The changes also imply a certain loss of innocence and the need to adapt to new, often difficult circumstances, as the characters no longer experience idleness but are instead filled with "keen, fierce vigor" due to the demands of their present situations.