I feel this is one novel which the age that you are when you first read it makes a large difference. Having read it when I was only a few years older than Ender was at the end, and believing myself to be very capable at that age, it seemed no large thing that those fighting the war and being pushed were children. In fact, to me, their maturity was not due to their intelligence, but took a large part from them being treated as if they had responsibility and as if they were capable of adult reasoning. Reading this book again, I still made those connections with Ender and the other "children". Although after what they have been put through, they seem to loose most of the behavior which would be expected from a 'typical' child. The contrast is most clearly expressed by Petra when after defeating the buggers and fighting a war, they will probably have to go to school when they get home because they're not yet 17. Graff also displace them from children as when he speaks to Ender towards the beginning, he places both himself and Ender under the category of tools for humanity, as long as humanity needs them.
One thing I particularly noticed this time through, was Graff's relation to Ender and Ender's corresponding inability to tell that Graff actually cared about him. Ender assumes, even when Graff makes an unnecessary and actually impromptu genuine gesture before they take off for Command School, Ender hardly has a doubt that it is just another move to manipulate him. What is surprising is how Ender doesn't probe further into what they are manipulating him for and doesn't suspect something more is going on. Although as he is being run to exhaustion and being completely isolated, maybe it shouldn't be surprising. Commenting on Ender's Shadow off Prof. PTJ's comment on Ender's Shadow with Bean figuring out more than Ender, from what I recall was due to him having more information and actually having people talk to him. I thought it was an interesting ending and helped draw a further parallel between the two boys.
(on a side note, this is what Tim and I found in Disney: