Ender's Game is the first entry of Orson Scott Card's successful and popular Enderverse. Goodreads Link: shorturl.at/cnKNO LibraryThing Link: shorturl.at/kBDEL Amazon Link: shorturl.at/cmDV3
I agree that is seemed unplausabable behaviour for young kids.. the bullying scenes of the brother and the language/psychology the kids used even though gifted was strange and I had to keep reminding myself to just enjoy it and not be puzzled by it so much. I enjoyed it and my 10 year old boy loved it too so the book did the job of being enjoyable for wide age range.
This is often a problem in media trying to depict children or juvenile protagonists. One instance would be that in A Song of Ice and Fire the younger characters (i.e. Ned's children) had to be "aged-up" for the TV adaptation, as it would have otherwise seemed to unrealistic. As I mentioned in the video, it kind of makes sense, since the children in Ender's Game have been chosen for their intellect, but it is really complicated to make it work properly.