From the 1916 census of Manitoba, Saskatchewan and Alberta:
Winnipeg, Manitoba
Willie Rothwell, 37, born England, immigrated 1910, accountant
Margaret E. Rothwell, 33, born England, immigrated 1910
Wm. J. Rothwell, 9, born Manitoba
Margaret Rothwell, 5, born Manitoba
Hazel Rothwell, 4, born Manitoba
The Manitoba Vital Statistics genealogy database has an entry for the birth of William Jesse Rothwell on 13 Apr 1907 in Winnipeg. His mother is listed as Margaret Edith Pill. There are no further details listed in the database. If you want to order a copy of the registration it costs $12 Canadian. Margaret and Hazel's births are not included in the database as they are still covered by privacy laws (births less than 100 years ago). Here's a link to the website:
http://vitalstats.gov.mb.ca/Query.phpFrom the Free BMD, there is a marriage listed from the first quarter of 1903 for Margaret Edith Pill that has Willie Rothwell on the same page in West Ashford, Kent (Volume: 2a, Page: 1779).
Jacquie