Robert is NOT the son of James & Mary (Blanchard) Sumner, although they may be related in some way. I have found the Will of James Sumner and his son Robert is mentioned as not yet being of age twenty one when the will was written on 026 Mar 1750. That said, I am assuming Robert's father was actually named William Sumner, as that was the name of he and Phebe's first born son. Will be researching further to determine Robert's parentage and will post my findings here once verified. If you would like to have a scanned copy of the original will of James Sumner, please email me.

Robert married Phebe (Beals) Canaday in 1746 in Fairfax Co VA, widow of Charles Canaday.

Children with Phebe:
1) William Sumner (1747-1801); m. Eleanor Edwards (b. 1749), d/o Hanuel & Eleanor (Scarfe) Edwards.
2) Bowater Sumner (1749-1829); m. Rebecca Burris (1760-1829), d/o John C & Esther (Terry) Burris.
3) Caleb Sumner (1751-1831); m. Mary Elizabeth (Cook) Carson (1748-1809), widow of Uriah Carson & d/o Thomas & Mary (Underwood) Cook.
4) Joshua Sumner (1753-1858); m. Sarah "Sally" Cox (b. 1760).
5) Phebe Ann Sumner (1755-1811); m. Welcome Garrett (1755-1811), s/o John III & Sarah Nancy (Bowater) Garrett.
6) Thomas Sumner (1756-1838); m1. Hannah Hiatt (1757-c1828), d/o Joseph & Hannah (Harrell) Hiatt; m2. Martha (Rich) Williams (1767-1851), widow of Ennion Williams, d/o John & Susan (Frazier) Rich.
7) Prudence Beals Sumner (1760-1835); m. Garrett Gibson (b. 1752), s/o Valentine & Elizabeth Gibson.
8) Abigail Sumner (1762-1854); m. John B Carson (1768-1840), s/o Uriah & Mary Elizabeth (Cook) Carson.
9) Sarah Jane Sumner (1765-1857)
10) Robert Sumner Jr (1767-1777)

At the time of their marriage, Robert was not a Quaker and the marriage was considered "out of unity," so Phebe was disowned by the church. On 26 Jun 1749, Robert joined the Quaker faith. The family was received at the Fairfax MM in Loudoun Co VA and Phebe was restored to the church.

In 1751, Robert moved his young family from VA to NC, where they became members of the Carver's Creek MM in Bladen Co NC in Feb 1751 and the Cane Creek MM in Orange Co NC in Jul 1751. Finally settling near Rowan Co (now in Guilford) NC, they were received into the New Garden MM in 1754.

One transcribed Quaker record says Robert died 1 Dec 1779, however, this is a mis-transcription and the 9 is actually a 5. See New Garden Quaker record, legibly dated 24 Feb 1776, whereby "this Meeting appoints Isaac Jones overseer in the room of Robert Sumner deceas'd". Also evidenced, Robert was deceased by the time his son Thomas married Hannah Hiatt on 8 Oct 1777.

Encyclopedia of American Quaker Genealogy
New Garden MM, Vol 1, Pg 22, NC:
"Thomas Sumner, Surry Co., son of Robert, deceased, m. Hannah Hiatt dt. Joseph, same place, 8-10-1777 [Oct 8, 1777] at Tom's Creek. Wit: David Ballard, John Jackson, William Beales, John Hiatt, Thos. Beales, Isaac Jones, Ann Hiatt, Ruth Jackson, Mary Carson, Sarah Beales, John Burras, Phebe Beales"

Source for children, dates and marriages:
Encyclopedia of American Quaker Genealogy
Vol 1, Pg 10, NC

Notes:
In 1742 Fairfax Co VA was formed from the northern part of Prince William Co VA. In 1757, the northwestern two-thirds of Fairfax Co became known as Loudoun Co VA. Do not yet know which exact area of VA Robert was born, but it seems to be Prince William Co.

Prior to 1752, Quaker records were read in the 'Old Style', using the Julian calendar; the first month was March and the last month was February. In and after 1752, dates were read in the 'New Style', using the present day Gregorian calendar; the first month is January and the last December.

Many, many thanks to Russell Kahn for the pictures!