Keep in mind, it's been many years since I read this. If I'm off or missing anything, please email me or comment! Thanks.
Language - Mild
OSC generally avoids the harsher swear words and chooses to pepper his with the ocassional h*ll, d*mn, b**ch, and b**tard. The only words I remember from this book were crude crotch references. (d*ck, b*lls.)
Sexuality - Moderate
As a prank a student programs the iPad-like "desk" to show male genitalia.
Boys make crude comments about Bean such as, "He could walk under my legs without even touching my b*lls."
Boys steal six-year-old Ender's clothes, forcing him to run around naked in public.
Violence - Moderate
Ender's brother Peter tortures squirrels and otherwise acts like a psychopath. His sister Valentine is scared for her life at points.
There's a lot of school-yard fighting. Fights are disturbing and even more so later when you learn....
(SPOILER!!!!).....Ender actually killed both of the boys he fought.
Mature Themes - A Few
A lot of bullying and various abuses of small children, kids outsmarting their (supposedly) less intelligent parents, locker room talk, and there's a whole political portion with Peter and Valentine that will go over the heads of younger readers.