I have nothing, in principle, against children serving. But I just can't see any concrete benefits and there are some serious downsides.

A big issue is that education needs to be done young. 17 or 18 is the age to get a degree because various abilities, especially in math and language, are still at their peak. I took a long time to do my degree because I was an undisciplined student so I saw my abilities, especially in math and memorization, decline rapidly after about 21. Having been in the military, I'd probably would be more disciplined if I started now, but for advanced education discipline just doesn't beat the sheer learning power of youth. And, at least in the Army, there is an anti-learning culture.

Young kids in the military are exposed to cradle to grave socialism. And if you do combat arms, you come out with virtually no useful job skills. (Really, what is an infantryman good for? Security?) So many guys get out and go straight into the government payroll working in the post office or law enforcement. If the military is the most conservative federal institution, that can only be because the rest of the government is to the left of Stalin.

And the military is the worst place imaginable to get laid for the first time. One kid I know went through (well, we all went through) a three year drama because the dumb jerk married a stripper. Another lost his virginity running a train. Even if you are smart and settle down, women just don't understand military life. They all think they do, but at any garrison you'll hear soldiers explaining into a phone, "no, I don't know when I'm getting home. No, there's nothing I can do about it."

Any pros? Discipline? You can learn that anywhere. Because the nation needs them? No, we don't. Because we want to mold them into the military mindset? To the extent that it does work, it just encourages mediocrity.