NEW : Two children were killed when a bus caught fire . NEW : Colombia 's President is in the area where the bus fire occurred . The bus was picking up children from a church , witnesses say . Authorities are investigating what caused the deadly blaze .
NEW : 31 children were killed when a bus caught fire . NEW : Colombia 's President is in the municipality where the bus fire occurred . The bus was picking up children from a church , police say . Authorities are investigating what caused the deadly blaze .