Who brings the presents on Christmas Eve night?
As the previous answer says 'It became a tradition in the US', I simply believe that this is untrue. Santa Claus brings presents on Christmas Eve ( I am also writing this answer on Christmas Eve!) because he simply wants to bring happy Christmas spirit in the hearts of families. It is also caused by a tradition by Jesus Christ, whose birthday is on this day. Jesus' presents were gold, frankencence and myrrh.
After dinner on Christmas Eve (most common in Europe) or Christmas morning (most common in USA). My family (in USA) opened Christmas presents at night after dinner on Christmas Eve. My wife's family opened them on Christmas morning. I like Christmas Eve better because the kids have all Christmas day to play with toys. Now that the kids are older (18 and 20), I still like Christmas Eve because I see the joy people opening Christmas presents one day earlier.