The tradition of having a nativity scene or "crèche" was made popular by St. Francis of Assisi. Saying a simple prayer such as this will help keep Christ in our hearts throughout the Advent season:
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. Amen