It's true. We have St. Francis of Assisi to thank for our creches. But did you ever wonder why every creche includes an ox and donkey in the set?
Brother Thomas de Celano tells us that Francis had earnestly desired to go to the Holy Land. It's another story to share why but suffice it to say that since he could not get to the Holy Land, he would bring the Holy Land to Assisi. So, in 1222, the Poverello of Assisi decided, while visiting the town of Greccio, to build a creche for Christmas.
Francis found his friend Giovani, who was a carpenter by trade and asked him to construct the creche. Giovanni asked what should be included in the construction. The Poverello asked for Our Lady, St. Joseph, the shepherds, and Magi. But when it came to the animals he had no idea. So, Francis said he would seek the Lord and consequently, spent the night in prayer. At sunrise, he thanked the Lord for His silence and prayed Lauds. The reading that morning was from Isaiah 1:1-10. After praying Lauds, he rushed to Giovanni and shared with him that the Lord had told him during Morning Prayer the two animals to include. It was Isaiah 1:3 that stood out which reads,
"The ox knows its owner, and the ass its master’s crib; but Israel does not know, my people does not understand.”
And this is why we have the ox and ass as part of our creche. And when asked why he created the creche, Bonaventure stated that St. Francis said, 
"I want to do something that will recall the memory of that Child who was born in Bethlehem, to see with bodily eyes the inconveniences of his infancy, how he lay in the manger, and how the ox and ass stood by."