BibTeX:
@incollection{Various,
  author = {Various},
  title = {Theresa Makes Bahá'u'lláh's Birthday a Special Day},
  booktitle = {Baha'i Stories for Children},
  url = {https://bahaistoriesforchildren.blogspot.com/2015/09/theresa-makes-bahaullahs-birthday.html},
}

APA:
Various. Theresa Makes Bahá'u'lláh's Birthday a Special Day. In *Baha'i Stories for Children*.

MLA:
Various. "Theresa Makes Bahá'u'lláh's Birthday a Special Day." *Baha'i Stories for Children*, n.d..

Chicago:
Various. "Theresa Makes Bahá'u'lláh's Birthday a Special Day." In *Baha'i Stories for Children*, n.d..