Final answer:
Francis P. Church's response to the little girl regarding Santa Claus is best described as an editorial, which expresses opinions and beliefs on belief systems and wonder.
Step-by-step explanation:
The published response given by Francis P. Church to the little girl asking about Santa Claus can be described as an editorial. An editorial is a piece of writing that expresses the opinions and beliefs of the writer or publication on a specific issue, often attempting to influence public opinion or discuss a relevant current issue. In this instance, Francis Church is taking a stand on the nature of belief and the importance of maintaining a sense of wonder and possibility beyond what is immediately visible or tangible.