A federal effort to arrest people who pay smugglers to bring children to the U.S. is prompting deep concern among advocates for those minors. Immigration and Customs Enforcement said its initiative aims to thwart human trafficking, and that people who pay smugglers are conspirators in a criminal operation — even if they are parents wishing to reunite with their children. Advocates for undocumented minors said this effort could re-traumatize children who have fled danger in their native countries.