Chesa Boudin, 28, is radical royalty. His parents are Kathy Boudin and David Gilbert, former Weather Underground leaders who were jailed after participating in the attempted robbery of a Brink’s armored car in 1981; two police officers and a guard died in the gunfire. He was raised by Bill Ayers and Bernardine Dohrn, perhaps even more prominent Weather Underground emeriti. He refers to them all as “my four parents,” as if it were the title of a dark sitcom.

Mr. Boudin was a toddler when the Brink’s job went awry. On the way to what became a deadly spectacle, his mother and father dropped him off with his Dominican baby sitter. He grew up, he writes in his new book, “going through a metal detector and steel gates every time I wanted to give my biological parents a hug.”

Mr. Boudin’s travelogue, “Gringo: A Coming-of-Age in Latin America,” is not about his parents, nor about growing up as far-left aristocracy. It is instead about the decade he spent crisscrossing South America, during summer vacations, semesters off, whenever he could. But his radical-chic background lingers like wood smoke or dense fog on each of this book’s 226 pages.

The product of militant politics and an elite education  he attended the University of Chicago’s private school and Yale, then won a Rhodes scholarship  Mr. Boudin arrives in South America as a stereotype: the comparatively wealthy gringo who’s come to bear witness to, and empathize with, the lives of the less fortunate.