Soldiers going in with child's medicine (11)
I believe the answer is:
expectorant
'medicine' is the definition.
(expectorant is a kind of medicine)
'soldiers going in with child's' is the wordplay.
'soldiers' becomes 'or' (Other Rank).
'going in' means one lot of letters goes inside another.
'with child' becomes 'expectant' ('expectant' can be a synonym of 'with child').
'or' inserted within 'expectant' is 'EXPECTORANT'.
(Other definitions for expectorant that I've seen before include "Cough medicine" , "something soothing from bottle" , "Cough treatment" .)