Hi! I emailed a response, but I'll post Robert and Polly's children here, too, in case anyone else is interested. Here is what I know. If anyone can add or correct anything, or if you would like more info, just let me know. Thanks! :o)
Robert McNair b. April 1778 in Tenn. or Ireland (census says TN) d. Oct. 1855, m. 1805 in Abbeville District, SC, to Mary Nicholas "Polly" Randolph b. 1784 Virginia d. Oct. 1854 Abbeville District. Their children are:
1. Lorenzo Dow McNair b. Oct 5, 1807, Abbeville District, SC, d. Oct. 24, 1878 Hinds County, MS, m. Feb. 4, 1835 Eliza Elianor Russell in Valley Creek, Dallas County, AL.
2. Louisa McNair b. June 26, 1809, Abbeville SC, d. July 31, 1887 Lebanon, Hinds County, MS, m. 1st George Washington Osborn in Abbeville, m. 2nd George Winkfield Prince.
3. Thomas Jefferson McNair, b. 1811 Abbeville, d. in Abbeville.
4. Alfred Randolph McNair, b. 1813 Abbeville, d. 1849 Abbeville. He was a doctor and his family stayed in Abbeville where he had a practice, but he also appears in Alabama with his brother (or so I've been told, haven't followed that up myself)
5. Lucinda Ellen McNair b. abt. 1815 Abbeville, d. Oct. 23, 1878 Hinds County, MS, m. Charles Edward Allen.
6. Sarah "Sally" McNair b. Dec. 12, 1817 Abbeville, d. Nov. 12, 1878 Hinds County, MS, m. 1833 James Hamilton of SC.
7. Eliza McNair b. Dec. 27, 1818 Abbeville, d. March 12, 1909 Hinds County, MS, m. abt. 1843 Edward Smith, Abbeville.
8. Gustava McNair, b. Feb. 27, 1819 Abbeville, d. July 9, 1879 Hinds County, MS, m. Mr. Stephens.
9. James Berry McNair, b. Jan. 16, 1821 Abbeville, d. Sept. 12, 1869 Hinds County, MS, m. Aug. 17, 1848 Susan Slater.
10. Elizabeth McNair, b. Oct. 4, 1822 Abbeville, d. May 31, 1862, Hinds County, MS, m. 1st J. Booker Hammond 1844 Abbeville, m. 2nd Mr. Clark.