。
Let's pretend to be soldiers.
Literal
We [topic-は] soldier [attributive-の] pretense [object-を] do-[volitional-よう]-[insistence-よ].
~のふりをする ('pretend to be X / act like X') is a common play/pretense construction, literally 'do the pretense of X.' 兵士 ('soldier'). The volitional よう + sentence-final よ invites peer participation — 'let's!'. A childhood-play scenario.