The United States isn't alone, nor has it pushed it as far as other places. Here's a little thing from Human Rights Watch -- the US never (at least in the last 100 years) used children as in its armed forces. And this list includes my own country, which, fortunately, is not stigmatised.

If a child, ANY child, is brought up in brutality and violence that child is far, far more likely to become a brutal and violent adult. The problem is not by any means limited to the United States, and anyone who thinks that it is is simply ill-read and ill-informed about the world and its problems.