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It would appear that Andrew Percival married Essex Blackwell at St. James Dukes Place, London, England on 7 October 1685. The records indicate that Essex Blackwell was christened 9 October 1643, making her 42 years old at the time of the marriage. An Andrew Percival was christened 3 July 1625, at Holy Trinity, Chester, Cheshire England. I am not sure this is the same Andrew, however his father, Thomas, b:1603) was the brother of Richard, b:1696, who was the father of Samuel, b:1619 (my ancestor). This would make Samuel and Andrew 1st cousins.
This is only speculation, however if you have any dates to match, it will help verify this.
Could Andrew have been married before and the children you mentioned be from a previous marriage in SC?