The two children were born between August 1911 (the latest we can see on the BDM NZ website) and August 1917 (the publication of the Reservists list).
Just noting Beg's statement above and questioning whether a "soon-to-be-born" child might have been included in the details provided by a Reservist ?
* The birthdate showing on NZ BDM (online) for Jean McMillan BLAIR, is given as "
13 September 1917" (so not yet born at the date of publication of the Reservists list.)
It may also be that the informant to the death of above lady, has made an error with "birth year" ?
Still worth checking microfiche birth index, to determine correct year of birth.
[And of course there's the possibility, this "Jean McMillan" is not related. ]

~ Lu