Not listed as a child of Robert Slaughter and Mary Smith, per the writings in Some Prominent Virginia Families Vol.4
https://books.google.com/books?id=3iQSAAAAYAAJ&pg=PA402&lpg...
All Robert's children were born in Saint Mark's Parish, Essex/Culpeper. The sons fought out of Culpeper in the Revolution and served/awarded land in Kentucky.
John was born in St. Peter's Parish, New Kent County, served out of Cumberland County and awarded land in Georgia. My instinct tells me he should be detached from Robert and Mary Slaughter.