This blessing can be conducted by any member of the family.
The family Nativity scene is a great way to remember the “reason for the season” and to place ourselves at that first Christmas day beside the manager. It’s one of the most beloved traditions of the Christmas season and is a perfect teaching tool for children.
Another way to heighten the spiritual meaning of the Nativity scene is to bless it using a blessing provided by the Church. Here is one that the USCCB prints on their website:
The leader prays with hands joined:God of every nation and people, from the very beginning of creation you have made manifest your love: when our need for a Savior was great you sent your Son to be born of the Virgin Mary. To our lives he brings joy and peace, justice, mercy, and love.Lord, bless all who look upon this manger; may it remind us of the humble birth of Jesus, and raise our thoughts to him, who is God-with-us and Savior of all, and who lives and reigns forever and ever. R/. Amen.
There is also a larger rite that includes various scripture passages that is found in the Book of Blessings.
However you integrate the Nativity scene into your family’s celebration of Christmas, consider invoking God’s blessing upon it so that it reminds you and your family “of the humble birth of Jesus and raise [your] thoughts to him.”
How to bless a Christmas tree