I notice you are confused. I think you've made two questionable assumptions;
Assumption 1. Wizard Children are not generally treated as competent at age 11.
Assumption 2. The children making the announcement at Hogwarts are responsible for brokering the deal. I.e. they aren't just mouthpieces for their respective families.
Assumption 2b. The Hogwarts staff is aware of 2.
Assumption 1 might be true - but I note that the age of majority has been increasing over time, and wizarding society is in many ways old timey. It seems reasonable to me that allowing a child of 12 to command a wizarding army is no stranger in wizard society than allowing David Farragut to command a ship at age 12 was during the war of 1812. Also, we haven't seen the reactions of the wizarding world in general - maybe everyone who isn't on the Hogwarts staff is scandalized. For that matter, maybe the staff is too, they're just not openly scandalized.
But assumption 2 seems completely wrong to me, and likely the main source of the confusion.
I notice you are confused
^ Don't do that.
No, I'm not assuming that children brokered the deal, but I can see that it may have looked that way, especially if you miss the context (that I was responding to the specific things EternalStargazer said).
To some extent, yeah, wizard children are, and are treated as being, more competent than muggle children. But there's still a very real difference between an adult and a child. For example, Harry Potter still needs a legal guardian. And I assume that McGonaggal's "She is a twelve-year-old girl, Albus!"...
This is a new thread to discuss Eliezer Yudkowsky’s Harry Potter and the Methods of Rationality and anything related to it. This thread is intended for discussing chapter 98. The previous thread is at nearly 500 comments.
There is now a site dedicated to the story at hpmor.com, which is now the place to go to find the authors notes and all sorts of other goodies. AdeleneDawner has kept an archive of Author’s Notes. (This goes up to the notes for chapter 76, and is now not updating. The authors notes from chapter 77 onwards are on hpmor.com.)
The first 5 discussion threads are on the main page under the harry_potter tag. Threads 6 and on (including this one) are in the discussion section using its separate tag system.
Also: 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26.
Spoiler Warning: this thread is full of spoilers. With few exceptions, spoilers for MOR and canon are fair game to post, without warning or rot13. More specifically: