Second child born 1918 in Belfast and died following day-Birth: https://civilrecords.irishgenealogy.ie/churchrecords/images/birth_returns/births_1918/01290/1534548.pdfDeath: https://civilrecords.irishgenealogy.ie/churchrecords/images/deaths_returns/deaths_1918/05197/4435893.pdfWhich leaves a gap between 1918-1921.Added- 59 Camden St., Belfast listed as tenements in 1924 directory.
James and Isabella had 2 other children. Jessie Cameron born 0ct 1st 1916 in Cork, and an unnamed daughter born March 4th 1918 in Belfast. You can see them in the Civil Registrations records on irishgenealogy.ie