I found the death record for Charlotte Young (nee Dunham). Is this the mother of Martha Young and siblings that you're searching for? When Martha married George Washington Hartwick the marriage record shows her parents as John and Charlotte Young, it also stated that Martha was born in East Gwillimbury and that she was living in Lindsay, Victoria Co. when they married.

Martha's mother:

Ontario, Canada Deaths, 1869-1932
Name: Charlotte Young
Death Date: 9 Dec 1919
Death Location: Rawdon, Hastings
Age: 82 years, 2 months, 9 days
Gender: Female, widow
Cause of death: Hemmorhage of the brain
Estimated Birth Year: abt 1837
Birth Location: Rawdon, Hastings Co.
Father: John Dunham
Informant: Frank Young, Stirling

1881 Census for Rawdon, Hastings Co.:

Charlotte YOUNG W Female German 45 Ontario Free Will C Baptist
Jane YOUNG Female German 17 Ontario Free Will C Baptist
Francis YOUNG Male German 20 Ontario Farm Lab. Free Will C Baptist

Source Information:
1881 Census Place Rawdon, Hastings North, Ontario
Family History Library Film 1375874
NA Film Number C-13238
District 122
Sub-district C
Division 2
Page Number 18
Household Number 90

Charlotte is a widow in the 1881 Census, her husband John Young had died prior to this time.

Audrey