This is a working research note which will change as I learn more. -- Wesley Johnston 18 Oct 2011
1851 Census of Kenwyn, CornwallThe widowed Ann (John died in 1844) is living with three daughters at Wheal Busy mine:
Ann - widow - age 51 [born c 1800] - Char Woman - born Kenwyn
Mary Ann - unmarried - age 18 [1833] - Work to Copper Mine - born Kenwyn
Emily - unmarried - age 16 [1835] - Work to Copper Mine - born Kenwyn
Harriet CHENHALL - married - age 22 [1829] - [no occupation] - born Kenwyn
1841 Census of Kenwyn, Cornwall
John and Ann and their children (minus William) are living at Greyhouse, which was in the parish of Chacewater (established 1828, formerly part of Kea). Keep in mind that the ages of those over 10 were rounded to the nearest 5 years in the 1841 census. All are shown as born in the County.
John - age 40 - Miner Copper
Ann - 40
John - 20 - Miner Copper
Elizabeth - 15 - Miner Copper
Harriet - 10 - Miner Copper
Mareyann -  7
Emeley - 5
Cornwall Family History Society Research Database - Baptisms
Searching in all parishes for B*S*N* with parents JOHN* and ANN* there are these baptisms found for the period from 1819 onward in Chacewater, Kenwyn (none) and Kea (none). The 1851 census calculated birth years and the differences are included in brackets.
BUTSON Elizabeth Dau BUTSON John - Ann Chacewater 7 Aug 1828 [not with mother in 1851 census]
BUTSON Emily Dau BUTSON John - Ann Chacewater 11 May 1843 [1835 - difference of 8 years]
BUTSON Harriet Dau BUTSON John - Ann Chacewater 28 Mar 1837 [1829 - difference of 8 years]
BUTSON J Mary Ann Dau BUTSON John - Ann Chacewater 15 Apr 1834 [1833 - difference of 1 year]
Keep in mind that these are baptismal dates and not birth dates: the children could have been baptized very young or baptized after reaching a certain age. Comparing these dates to the 1851 census, it does indeed appear that they waited until the children were 8 years old to have them baptized. Mary Ann is an exception to this.
There are also these baptisms at Gwennap, which are apparently theirs:
BETSON John Son BETSON John - Ann Gwennap 25 Jul 1822 [not with mother in 1851 census]
BUTSON Mary Ann Dau BUTSON John - Ann Gwennap 28 Feb 1832 [This would apparently have been a prior Mary Ann, who probably died before the birth of the one who was baptized 15 Apr 1834 at Chacewater.]
BUTSON William Son BUTSON John - Ann Gwennap 6 Apr 1823 [not with mother in 1851 census]
Cornwall Family History Society Research Database - pre-1838 Burials
The following BUTSON burials were found at Chacewater. The search for B*S*N* also found 8 BASTIAN/BASTION and one BENSON burial.
BUTSON Mary Ann 2 May 1834 2 1832 Wheal Busy Chacewater
BUTSON Mary Anne 17 Jun 1832 1 1831 Wheal Busy Chacewater
BUTSON William 17 Jan 1837 1 1836 Cox Hill Chacewater
BUTSON William Luke 12 Jan 1835 2 1833 Cox Hill Chacewater
If these were children of John and Ann, then it means they had three children named William and three named Mary Ann, losing all three of the Williams and all but the last Mary Ann. However I have not yet researched to find out if these may have been children of the other two Butson families then at Chacewater (William & Peggy [NORTHEY] BUTSON and Edward & Mary Ann BUTSON).
Death Record of Harriet Ann (BUTSON) CHENHALL
Since she was 91 years old when she died, the information in the death record of Harriet Ann BUTSON, under her married name CHENHALL, at Owen Sound, Ontario 11 May 1919 is clearly suspect. But it must be addressed.
AGE - 91 years 3 months 21 days -- This calculates to a birth date of 20 Jan 1828, which is consistent with her age (22) in the 1851 census.
PLACE OF BIRTH -  Whitehall, England -- There was a Whitehall in Kenwyn, which is where the 1851 census shows her birth, although she was baptized in Chacewater at age 8.
PARENTS - W. J. BUTSON and Elizabeth TREVETHAN -- The W in John BUTSON's name appears in no record. And Elizabeth TREVETHAN is completely absent from any records of the family, so that it is unknown how the informant on the death record believed this to be Harriet's mother.
Current Summary
1 - It does appear that their son William died prior to the 1841 census. More research is needed on this.
2 - It also appears that they may have had more than one daughter Mary Ann and more than one son William, as new babies may have received these names when the prior ones died. More research is needed on this.