hmm,I think theory should be a smaller board under composition, myself, because without composition, there would have never been any theorists =)
Sounds good to me. I'm not really concerned about the hierarchy. I don't see child forums as being "lesser important" or dependent on the main forums anyway.
Music Theory is hardly depends on students either.

I can see why it was put there as a child forum though. It's assumed that students would be interested in learning music theory. However, teachers may wish to discuss how to teach music theory too so it could have just as easily be a child to the Teacher's Forum.
I just think that both Composing, and Music Theory, are topics that would be of interest to everyone, not necessarily just students. But I would also think that they would be closely related. By that, I mean that I think most composers would be interested in music theory, and people who are interested in music theory might also be inclined to take a stab at composing.
In any case, I think there should be a Composing Forum no matter where they actually put it. And it just seems to me that music theory should be easily accessible to that forum. I actually see no problem with having two Music Theory forums. Perhaps one as a child to the Student Corner Forum, and one as a child to a Composing Forum. I say this because students may have question about learning music theory, whilst composers may have more advanced questions concerning various aspects of how to apply music theory, or use it analytically.
Just my thoughts.
I would be very happy to see a Composing Forum so this thread holds interest for me.