Did I do some searching for you before on this family as it sounds familiar?
There is a baptism for William Eric, which says: son of William John Mander of the City of Montreal and of Mary Jane Scollace, his wife,w as born on the 24th day of July A.D. 1920 and was baptized on the 10th day of May A.D. 1940.
So it may be he wanted to be baptized before he left for War.
Quebec, Vital and Church Records (Drouin Collection), 1621-1967 about Mander Name: Mander Event: Baptême (Baptism) Baptism Year: 1940 Baptism Location: Montréal, Québec (Quebec) Place of Worship or Institution: Anglican, Saint Philip (Montréal-Ouest)
Do you need the baptisms info for Alfred Henry in 1916 also ? There is also a baptism for a child of Alfred Henry and Alice Mary Brown - child named Desmond William.
There is a marriage for William John Mander and Cinderella Maud Philipps in 1915 - I can give you these details also if you don't have them - he is indexed as Muader
There is also a burial for an Ann Hammerton Mander (indexed as Mauder) who died 1924,wife of the late William Henry Mander. Witnesses were William John Mander and Alfred Henry Mander
** could this be the Annie you mention who came with her daughter Ethel
*** I think it must be her as I just found birth of Ethel Maud Mander showing father as William Henry Mander and mother as Annie Hamerton Mander
Warwickshire, England, Baptisms, 1813-1910 about Ethel Maud Mander Name: Ethel Maud Mander Parish: Kenilworth Baptism Date: 13 Oct 1886 Father's Name: William Henry Mander Mother's Name: Annie Hamerton Mander
Also other children
Warwickshire, England, Baptisms, 1813-1910 about William John Mander Name: William John Mander Parish: Kenilworth, St John Baptism Date: 5 Feb 1888 Father's Name: William Henry Mander Mother's Name: Ann Hamiston Mander
Warwickshire, England, Baptisms, 1813-1910 about Alfred Nows Mander Name: Alfred Nows Mander Parish: Kenilworth, St John Baptism Date: 2 Mar 1890 Father's Name: William Henry Mander Mother's Name: Anne Humdlx Mander
But I have not had any luck in finding Ethel Maud or Jack after their 1916 arrival date.