U.S. immigration enforcement officers are proposing that fingerprints be taken from all people claiming custody of children who have entered the United States illegally without an adult relative, a measure that opponents said could keep thousands of families apart. As a new wave of unaccompanied Central American children pours across the U.S.-Mexico border, the proposal underscores the sometimes conflicting goals of federal agencies in dealing with undocumented immigrants, a volatile issue on the presidential campaign trail. Officials at the U.S.