Hello Liz, I have found on 1881 Census,

Source Information:
Census Place
Onchan, Isle of Man, Isle of Man
RG11 Piece / Folio 5604 / 77 Page Number 20

Dwelling 13 Frederick Street

John CAIN Head M Male 52 Isle of Man,England Laborer (General)
Catherine CAIN Wife M Female 60 Isle of Man, England
John CAIN Son Male 13 Isle of Man, England Grocers Shop Lad
Elizabeth CAIN Daur Female 11 Isle of Man, England Scholar
Annie CAIN Daur Female 10 Isle of Man, England Scholar
John James CLEATOR Lodger U Male 24 Isle of Man, England Tailor
Henry S. KELLY Lodger U Male 21 Isle of Man, England Blacksmith
John T. RADCLIFFE Lodger U Male 22 Isle of Man, England Tailor

MAYBE the Son, John c1868 is the, John Cain you found on the 1918 Electoral Roll,

Averil