According to Stanley Corey in his book - Some Descendants of Nicholas Rideout and Sarah Oliver Rideout of Maugerville, N.B. - page 10 - "Rebecca, b. 1804 (1861 census); m. Thomas Whitefield (or Whitfield) 22 Oct. 1823 (York County rec.) Thomas died 2 April 1847, and in 1861 Rebecca was living in Brighton Parish with two sons: William C. Whitefield, b. 1838; a schoolmaster and a widower in 1861. Alfred Whitefield, b. 1841 It would seem that there should have been children born between the date of the marriage and the birth of William, but a search of the printed census of 1851 of Carleton County failed to find any who would qualify."
You mentioned the family had moved to Ontario. Perhaps any other children stayed there.I would be interested in any other info you might be able to provide. I, too, am a descendant of Nicholas and Sarah, but through their son, Oliver.