The Four Unknown Blackwell Children are John Blackwell's children he had with unknown women, apart of the Circle and outside of Chance Harbor. They are also the paternal younger half-siblings of Cassie Blake, and Diana Meade, Those kids possess Dark Magic.
They are all members of the Blackwell Family.
The four children were conceived and born right around the time Cassie Blake and Diana Meade were. It appears that there are three boys and one girl. John Blackwell had planned to kill all witches without Balcoin blood, seeing them as the superior race of witches using Dark Magic. He had planned to unite his six children to create a Dark Circle, each of them branded with the mark of Balcoin.
In Family, Jake Armstrong's grandfather, Royce Armstrong sent him a note and a bracelet with some kind of bottle filled with white beads inside and the note said that the circles are coming together and that their fight was far from over, thus implying that the Blackwell siblings were coming to complete their father's task. At the end of the episode, all four of them were standing on-top of a cliff, looking down into Chance Harbor, revealing that they have already arrived at the end of the episode with The Blackwell Symbol on their hands.
- Unnamed Female
- Unnamed Male 1
- Unnamed Male 2
- Unnamed Male 3
- It is unknown if the four children are descendants from the twelve families of Salem that stayed East after the Burning Times, though it's highly possible.
- John Blackwell knew who they were and reached out to them.
- According to John Blackwell, he's summoned his other four children to Chance Harbor to bind a Dark Circle with only Balcoin blood with Cassie and Diana.
- It is possible that they are far more skilled and more experienced in using Dark Magic than their two half-sisters, Diana and Cassie, as their father taught them dark magic.
- In the books, Cassie has only one half-sibling. Scarlett. Diana is not her sister either in the books.
- It is unknown if they are all good or evil.
- Their names are unknown.
- According to John Blackwell, these children were all brought up in different Circles.