Stjärngossen
..and 'Staffansvisan' - in any way connected to Lucia? Not really. The stjärngosse [Star boy], though not always a popular tradition with boys today, has his most likely origin in Catholic times and is, from its beginning, related to Epiphany rather than Lucia. When Sweden was Catholic (until Protestant Reformation in the 1500s), mass was held in Latin and common people didn’t understand much of the sermons. For Epiphany the church used to arrange for a play to make it more understandable for churchgoers, with a dramatization of kings arriving to Bethlehem led by a boy carrying a bright star to guide them.

And as for the “Staffansvisa,” in another, slightly tweaked interpretation of legend, the star boy represents “Staffan,” the holy Stefanus, one of the first Christians in history. According to this, Staffan was King Herod’s stable hand at the time of the birth of Christ. As he saw the star after the birth Staffan supposedly exclaimed that a larger king than Herod had been born. Herod, who according to history stoned all first-borns of Bethlehem at the time, became so angry that the young boy was stoned.
Saint Stephan is only mentioned in the New Testament, however, as a deacon in the early church of Jerusalem; he was stoned after defending his faith later in life. Saint Stephan is venerated as a saint and considered the first martyr of Christianity. December 26 is St. Stephen’s Day, the "Feast of Stephen."

More on the tradition of Lucia in Sweden: Swedish Lucia, the Queen of Light

Or, Swedish Christmas - The season of light