Michael Clark was the unborn son of Randall Clark and Sylvie.
After confirming Sylvie story (it matching the "interrogations" of other captured survivors the year prior) they started a relationship with each other. She not knowing how to survive outside of a Vault but wanting to learn. By September 9th, 2100, the relationship blossomed and she was pregnant with Clark's child. Unfortunately their son Michael was born breech, Clark tried to turn him and failed. The Caesarean was a failure and she never regained consciousness. He buried them both south of the narrows. Being by their sides comforted him, as before he never go to say goodbye.