A search of free bmd does not reveal any children from 1918 to 1940. The 1939 Register suggests that Christina was ten years older than William. Is that correct?
There appears to be a death for Christina in June quarter 1958, birth year given as 1879.
It also looks as though William J N H remarried in 1958 to a Gertrude R Glendinning. Marriage registered in the March quarter. So before Christina's death??
I don't know what else you know about William and Christina so don't know if any of the above is correct.