In "The Gift of the Magi," who were the three wise kings?
You have asked an excellent question that goes to the very heart of the meaning of this excellent short story. The Magi referred to in the title of this story are the three "wise men" who, according to the Bible in Matthew 2:1-13, brought gifts of frankincense and myrrh as well as gold to the infant Jesus. Traditionally the Magi's gifts are regarded as the first Christmas presents.
Now, of course, what you need to do as an active reader of this short story is consider why the author makes this allusion. Note how in the last paragraph the author explicitly makes a link between the couple, the "foolish children" as he describes them, who "most unwisely sacrificed for each other the greatest treasures of their house." Yet note how the story finishes and what the author says about this couple:
But in a last word to the wise of these days, let it be said that of all who give gifts, these two were the wisest. Of all who give and receive gifts, such as they are wisest. Everywhere they are wisest. They are the Magi.
The author thus draws an explicit link between the feelings and emotions behind the "foolishness" of this couple and the original intention behind giving gifts as modelled by the Magi. His final declaration of "They are the Magi" seems to show that those who give gifts, however foolishly, with real sacrificial love behind them, are worthy to be remembered and really show what gift giving is all about. This is how the allusion to the "wise men" in the birth narrative of Jesus operates.