Luke 2:8 "In the same region there were some shepherds staying out in the fields and keeping watch over their flock by night."
John MacArthur notes that "Bethlehem was nearby Jerusalem, and many of the sheep used in the temple sacrifices came from there."
So... the shepherds were "parenting" the sheep who would portray the Lamb of God in the visual enactment of the Messiah's forthcoming death. The reality was happening nearby. How thoughtful of the Lord to allow the Symbols to go and witness the Substance of the part they were playing!