Is everyone in the army a Wuss?
If I had to choose between shooting a kid and losing the entire country (and all of EUROPE) to a highly contagious virus, I'd sure has hell shoot the kid right in the FACE. The order was "All targets are free. NO EXCEPTIONS". What about "no exceptions" don't you understand??
"Ohhhhh but it was such a cute little boy and I like little children so I spared him"
Humanity FAILED in this movie. Or maybe the writer did? I don't know.