I am not convinced that Patrick and Eliza were married. I am thinking that perhaps they listed Patrick as the head of the household since in fact he was the elder.
The person taking the census may have assumed Patrick and Eliza were married.  It seems to me that Frederick was actually closer in age to Eliza and quite capable of
fathering children over this period of time. It is possible that the error was made on several census forms. Frederick remains on the census forms for 1871 and 1881.
The only way to verify the father would be to find a birth certificate or baptism certificate for the children.
Additional Note: An Andrew Donohue (Born: 1834 Newfoundland) was found in an 1881 Canadian Census. At the time he was located in BC working as a hotel keeper. If this is one of Patrick's sons Patrick would have been 28 at the time.
Patrick Donohue 1806 Ireland - landed in Newfoundland, may have left after death of first wife (spelled Donohoe on census)
Eliza Donohue 1845 Ontario (must be second wife)
Frederick Donohue 1843 - Newfoundland
Charles Donohue March 12, 1847, Newfoundland
Agnes Catherine Devoy September 12,1857 Ontario
Charles Frederick Donohue b: July 25, 1875
Lived in Windsor, never married. He was engaged to marry, bought his wedding suit
while he was away. Upon his return he found that his bride to be had died.
Robert Donohue 1878 US d: June 19, 1947
Maud Rockwood 1879 d:  1947
m: august 29, 1900 d/o James Rockwood and Mary Lee
witness Joseph Hill and Mary Donohue    
Robert Clifford Donohue b: May 15, 1903
James Vernon Donohue b: October 14, 1903
Fergus Orten Donohue b: December 13, 1905
Benard V.C. Donohue
Mamie (Mary Ann) Donohue b: March 22, 1879 US
m.John Miller (? D: 1948) Move to Lubbock Sask,
No Children
Bertha Donohue b: April 27, 1881
On a 1881 census bertha was listed  as being 3 months old. She must have died
Between 1881 and the next census 1891. She was no longer listed.
Julia Donohue 1883 Ontario d: Feburary 20, 1897
Edward Donohue b: October 23, 1885 Ontario d: March 19, 1923
Alice Tamblyn b: August 6, 1887 d: September 13, 1977
Ella Donohue b: 1915 d: January 2, 1995
Robert Carly
Edred Donohue b: July 3, 1920 d: 1931
Heart problems, buried St.Mary's Gate
William Donohue b: August 25, 1887 Ontario
Ruby Granger b: 1895 d: 1918
Donald Donohue Ontario
Hilda Manship Born:  1914 London Ontario, died: February 17,1984
Shannon Donohue
William Donohue
Donald Donohue
Evelyn Donohue
Lenore Donohue Ontario (b: 1905, Died: March 10,1993 buried: Mt. Pleasant )
James Crawford Still alive
David Crawford
Norma Donohue Ontario (b:?, still alive)
James Schmuck
Five Children
Mabel Lillian Donohue b: August 25, 1889
Henry John Kaltenbach b: 1888 s/o Frank Kaltenbach and Elizabeth Thompson
m: July 29, 1908
Arthur Donohue b: December 16, 1891
Ettie (Etta) Donohue b: December 28, 1892 d: 1983
Robert Alfred Bear b: November 24, 1888 d: August 1970
m: November 12, 1909
Ronald Bear
Leona Bear
Mabel Lillian Bear
Nelly Perial Donohue b: December 28, 1894
Mary Donohue b: February 20, 1896 d: September 13, 1991
Ed Carrol Moved to windsor
Cecelia Carroll b: 1912
Helen Carroll b: 1913 d. May 23, 1918 London
Annie Carroll b: 1914
Charles Carroll b. 1915/1916 d: March 1, 1916
William Carroll b: 1917
Alberta (Berta) Carroll b: 1920
Cecil Carroll b: 1922
Leo Carroll b: 1924
(1) Anne MacDonald b: 1925 d: 2000
Had 2 children
(2) Gwen (MacDougall) Lefton b: 1928
Gwen has 4 children from a previous marriage
Daniel Carroll b: 1925
Frederick Carroll b: 1927 d. 1983
Francis (Frank) Carroll b: 1928 d: 1997
Dorothy Carroll b: 1930
John (Jack) Carroll b: 1931
Theresa Carroll b: 1932/1933 d: 1932/1933
Mary Carroll b: 1935
Michael Carroll b: 1936
Gloria Carroll b: 1939
Robert Carroll b: 1940
Leo Joseph Donohue b: November 1, 1897 (1899?)
James Donohue 1864 - Ontario on an 1881 census James was listed as a servant working for Joseph Matheson and Family (he was 17)
Ellen Donohue 1866 - Ontario
Patrick Donohue 1867 - Ontario
Henry Donohue 1870 - Ontario
William Donohue 1872 - Ontario William and Marg were found listed on an 1881
Marg Donohue 1874 - Ontario census found on familysearch.org
These dates are give or take a year
the year depends on the accuracy of the census,
when it was taken and the age at the next birthday