Your tree is almost identical with the familysearch.org tree, with the exception of the spelling of Cavanaugh versus Kavanaugh & the familysearch tree has more details for this family. Please look again and do a comparison. I am not related but would hate for you to pass up an opportunity to learn more.
Your tree is here: debgeof
http://trees.ancestry.com/tree/41167055/person/19587142091the familysearch.org tree is here:
https://familysearch.org/ark:/61903/2:2:3WPC-LJ7Most of the so-called 1851 Census was done during the first quarter of 1852, if you look on this census for this family, on the previous page, the date of the census was January 1852.
I know that James' death register named his mother as Mary Downey of Co. Kilkinney, Ireland, & father as Garrett b. Co. Carlow, Ireland
the informant was: T.T. Kavnaugh of Alex. Bay, NY; however, look at the following records to see what the mother's maiden name was listed as:
Name: James Kavanagh
Gender: Male
Christening Date: 03 May 1841
Christening Place: Saint Francis Xavier, Brockville, Ontario, Canada
Father's Name: Garrett Kavanagh
Mother's Name: Mary Mullorony
Name: Bridget Kavanagh
Gender: Female
Christening Date: 10 May 1843
Christening Place: Saint Francis Xavier, Brockville, Ontario, Canada
Father's Name: Garrett Kavanagh
Mother's Name: Mary Muldowny
Name: Bernanr Mcnamee
Birth Date: 1834
Birthplace: Bastard
Age: 25
Spouse's Name: Bridget Kavanagh
Spouse's Birth Date: 1843
Spouse's Birthplace: Canada
Spouse's Age: 16
Event Date: 08 Nov 1859
Event Place: Leeds And Grenville, Ontario
Father's Name: Partick Mcnamee
Mother's Name: Rose Johnston
Spouse's Father's Name: Garet Kavanagh
Spouse's Mother's Name: Mary Mallory
Name: James Kavanagh
Spouse's Name: Julia Fenton
Event Date: 18 Nov 1867
Event Place: Brockville, Leeds, Ontario, Canada
Father's Name: Garret Kavanagh
Mother's Name: Mary Muldowney
Spouse's Father's Name: Bartholomew Fenton
Spouse's Mother's Name: Mary Walsh
Name: Thomas Kavanaugh
Event Type: Marriage
Event Date: 20 Nov 1873
Event Place: Brockville, Ontario, Canada
Gender: Male
Age: 27
Birth Year (Estimated): 1846
Father's Name: Garret Kavanaugh
Mother's Name: Mary Muldoon
Spouse's Name: Mary Elizabeth Dollinger
Spouse's Gender: Female
Spouse's Age: 19
Spouse's Birth Year (Estimated): 1854
Spouse's Father's Name: Lewis Dollinger
Spouse's Mother's Name: Jane Daly
Name: Andrew Kavanagh
Spouse's Name: Catharine Isabella Nolan
Event Date: 02 Jun 1875
Event Place: Saint Francis Xavier, Brockville, Ontario, Canada
Father's Name: Garret Kavanagh
Mother's Name: Mary Muldoon
Spouse's Father's Name: James Nolan
Spouse's Mother's Name: Mary Bolger