Do you know if Mary was sent to Canada under the Home children scheme. https://www.canada.ca/en/library-archives/collection/research-help/genealogy-family-history/immigration/home-children.html
It would be almost impossible to find any children she had that were adopted, there were no official adoption records in England until after the Adoption of Children Act in 1926 and a 3rd party would not be able to access any records after 1926 unless they met certain criteria, you would also need names. Prior to 1926 illegitimate children were often adopted or raised within a family, fostered out or "adopted" through various organistation, charities.