Cute little guy!
I believe there is another possibility too, besides reincarnational tendencies.
I hypothesize that besides our five sense interface with the physical reality, we are also in contact with it at nonphysical level, more even than just telepathy. While the nonphysical contact with the other participants in the physical reality happens at any age, for everybody, during childhood we (our egos) are less conditioned by our society's beliefs, and more aware of what others think and focus on.This allows the child to faster learn and adapt to the new (physical) reality framework.
Under this hypothesis, it is possible that some of the little guy's unexplainable military like gestures to have been perceived non physically from others, who are close to him, and to whom he pays more attention, one or more people interested in military.
I guess the gift of that military outfit wasn't just a random choice.
Maybe you could ask him directly, without planting any leading suggestions, how he came with the idea for those military gestures, where they came from.