[FOX] Former Homeland Security Secretary Kirstjen Nielsen and a top immigration official challenged a previously secret White House plan to arrest thousands of migrant parents and children in nearly a dozen U.S. cities, Fox News confirmed Monday.The Trump administration wanted to target migrant families that had crossed into the U.S. from Mexico in attempt to show that the U.S. wasn't going to back down on its border stance by detaining and deporting illegal immigrant families, The Washington Post first reported, citing several current and former Homeland Security officials.