The Children of the Son were an minority religion emerging on 892-IV in the mid-23rd century, very similar to Earth's early Christians who often lived in hiding from the Roman government. Unlike on Earth, the religion started to spread in their equivalent of the 20th century. Upon learning of the Children, the crew of the USS Enterprise initially confused the name for "Children of the Sun", and believed them to be a cult of sun worshippers.
The religion centered on the Son, an analogue to Christ. Their philosophy was referred to as the "word of the son", and emphatised total love and total brotherhood. All men were considered brothers, and might even call themselves or others such. They had a concept of heaven, which was where the son was. The stars were believed to be lights shining through from heaven. Its adherents believed it to be the only true belief, the Roman deities being false gods.
The children of the Sun were heavily persecuted. One adherent named Septimus was a senator, but was made a slave upon converting. It was most popular under the slaves, and when slaves began to worship the son they became discontent. Spock believed the Children of the Sun where destined to replace Roman culture in less than a century. (TOS: "Bread and Circuses")