In Julia Alvarez's book, In the Time of Butterflies, there are several symbols.
First, as noted in the title, butterflies are significant. (This supports the theme of "change and transformation.") In the history of the Dominican Republic, Rafael Trujillo was a feared and violent dictator. In the face of his oppression of his people, a secret resistance was born: three of the members of the resistance were...
Las Mariposas, or The Butterflies. These were the code names of Minerva, María Teresa, and Patria Mirabal, three sisters who were key members in an underground movement to overthrow Trujillo.
In this story, the women represent a fight for freedom from oppression. The image of butterflies would symbolize, then, the metamorphosis of these young and innocent girls into courageous women (who ultimately die for their cause). In addition, butterflies could also symbolize the freedom for which these women struggle: not only for themselves, but for the entire country.
Another symbol could be the children. The children are a symbol of hope for the future, and also for the legacy of their parents that they carry into the future. They symbolize generations to come, and it is for them—the children and future generations—that Minerva, Maria Teresa and Patria fight.
Another theme is authoritarianism. I believe that Trujillo not only is a dictator in his own right, but can be thought to symbolize the abuse of power in any region/country, etc., where an authoritarian government rules, controlling the people in every aspect of their lives. The dangers that Alvarez points out show how a tyrant can affect not just the actions and thoughts of the adults, but can also serve to brainwash the children, a threat to generations to follow—the future, in this case, of the Dominican Republic.