The Purification of the Blessed Virgin Mary
In the Law of Moses, a woman who bore a son was ritually unclean for 40 days (Leviticus 12). The artwork shows St. Joseph holding two turtledoves or pigeons (Luke 2:24). The Holy Family could not afford a lamb, so they offered these for the purification ritual (Leviticus 12:8). Though the Blessed Mother had no sins to repent, she fulfilled the Law.
The Presentation of the Temple by Philippe de Champaigne oil on canvas painting in 1648
If the Magi offered frankincense, gold, and myrhh, why couldn’t the Holy Family afford the lamb?
The visit of the wise men does not take place immediately following Jesus’s birth. In fact, the visit seems to have taken place a year or even two years after the birth of Jesus. Hence when Matthew gives his description of the wise men showing up in Bethlehem (see Mt 2:1-12), we need to understand that this is taking place a good while after the nativity, even though most of us tend to merge these events together in our imaginations!
As for the idea of Jesus already being one or two years-old when the wise men arrive, this is indirectly corroborated by the infamous edict of Herod, which only occurs after the wise men have visited: “[H]e sent and killed all the male children in Bethlehem and in all that region who were two years old or under” (Mt 2:16).