The child of William Charles Corrin & Annie closest in age to the one you have given for William Henry was Walter Bromley Corrin b.6 Oct 1879, regt Douglas (Brian Lawson's births index).

Where was Walter in the 1881 census?
[He didn't die until 1908, buried aged 28 in Braddan, 23 Apr (Brian's burials).]

Another child was born in Sept 1882, regt Douglas, so Wm Henry (ag. 9 in 1891 census) must have been born in mid/late 1881.

Incidentally, the IGI has Annie's surname in an extracted marriage record as COWIN, not CORRIN (Brian's births). 15 Jan.1876 Braddan.
You need to look at the original records, both the marriage and at least one of the births, to find her correct name if you haven't already done so.

Sue