WASHINGTON -- President Barack Obama and First Lady Michelle Obama will welcome elementary school students from 17 area public schools to the White House on Saturday for Halloween trick-or-treating. The event marks the third time the Obamas have opened the White House for Halloween. Joining the elementary school kids will be students who attend local Boys and Girls Clubs, as well as children of military families.The columned White House North Portico, often considered the facade of the house, will be lit orange for the occasion.