One of the more disturbing angles of the Civil War is the number of child soldiers on both sides.
https://en.wikipedia.org/wiki/Child_soldiers_in_the_American...
https://en.wikipedia.org/wiki/Child_soldiers_in_the_American...
For example, Roman life expectancy was only 21, but if you made it to age 5 it jumped to 42.
Even then the laws at the time was 18 to enlist -- so they already viewed child soilders the same way we do now. The big difference is age verification was a lot harder because there was little in the way of a paper trail.