An obvious concern is finding quality actors at such a young age and while Ender is only 5 when he’s recruited, that’s obviously an incredibly difficult age to cast for such a crucial and “smart” role. The script indicates that Ender is 10 instead of 5. While this is a significant jump in age, it’s an understandable change.
Ender Wiggin: He’s depicted as smart and sensitive, but also incredibly ruthless. There are a few scenes where he worries about being like his cut-throat brother Peter, and confides in his sister Valentine. Just like in the book, he dishes out a rough treatment to Bonzo Madrid, his former platoon leader, when Bonzo tries to bully him too much. And then he feels bad about it. The screenplay also includes some scenes where Ender has weird nightmares about the buggers — and he tries to understand where the buggers are coming from, and what their children are like. Ender is pissed at Graff because he keeps changing the rules in the war “exercises.”
The scene where Ender finds out that his final victory was not, in fact, a game is pretty intense, and features Ender and Graff both trying to talk at the same time. Ender is saying “They came to establish a colony, we chased them away… in fifty years they have never returned,” while Graff is saying, “It makes no difference now,” and then Ender is saying “Now I am become death, the destroyer of worlds,” at the same time as Graff is saying “What are you talking about?” Finally, Ender is saying “I will bear the shame of this xenocide forever,” at the same moment as Graff is saying, “You will be remembered as a hero.” It ends with Ender getting an injection, knocking him out.
Bean: We get to see Bean watching a heavily edited video of Mazer Rackham’s famous victory over the formics, in which Mazer fires his nuclear warhead into the formics’ exhaust system. And Bean is so thrilled he throws his hands in the air and shouts with joy — until Ender bursts his bubble, explaining that the video is edited so we don’t see Mazer die. (And later, Ender also hints that Mazer’s victory might have had a darker side, that’s also edited out.) In another scene, Graff shows Bean and Ender to the famous zero-gravity training room, where they float around with a bunch of other kids. Ender explains to Bean that there’s no “up or down” in zero-G, and then they discover their weapons actually freeze anyone they shoot at, by causing the spacesuits to swell up. They team up to go freeze some of the other kids.
Peter Wiggin: Ender’s brother is fully a psychopath in this version of the screenplay. He’s insanely jealous that Ender was chosen for the battle school, and completely enraged when it seems like Ender has washed out of the program. At one point, he locks their sister, Valentine, out of the room and forces Ender to put on a Formic mask so they can play Formics and Astronauts, which basically consists of Peter beating the crap out of Ender.
Valentine Wiggin: She’s the gentler, sweeter member of the Wiggin family, who’s always there for Ender — except for when the people in charge of the school won’t let Ender communicate with her. She tries to protect Ender from Peter, but mostly fails — and just like in the book, she convinces Ender to return to the school when he tries to drop out after he hurts Bonzo Madrid. She explains to Ender that what makes us human is our brains, and we didn’t evolve those brains so that we can lie around lakes — we evolved them for killing, or else we wouldn’t still be around. We’d have been killed by wild animals. She alone grasps that Ender has to understand his enemy to defeat them, and in understanding the enemy, he grows to love the enemy — right before he destroys it.
Bonzo Madrid: Just like in the book, he’s a swaggering idiot whose platoon has won most of its most recent battles, and he resents being saddled with a useless, untrained snot like Ender. He orders Ender to stay out of the way during battles, and not even use his weapon. Later, he takes a group of his homies to try and ambush Ender in the shower.
Rose the Nose: The commander of Rat Army, where Ender gets traded after he leaves Bonzo’s toon. Rose has a high opinion of his own leadership skills, even though he knows that his platoon leader, Dink, is “God.” Rose has a terrible fear of losing, but can’t face the fact that he’s winning thanks to Dink and Ender.
Dink Meeker: In the script pages we read, Dink is one of the characers who befriends Ender in the Rat Army, helping to protect him a bit and showing him how to go float in the zero-G chamber to relax.
Petra Arkanian: The only girl in Ender’s first toon, she also befriends Ender and tries to protect him — and when Bonzo decides to keep Ender out of combat, Petra offers to help him train in their spare time. Later, she and Dink are both in Ender’s Jeesh, and she’s a key part of the final assault on the bugger planet.
Alai: Just like in the book, he’s a gentle Muslim boy who moves Ender with his friendship and his professions of peace.
Mick: He’s a heavyset boy who just wants to make it through this school in one piece and get home — and he’s happy to help himself to other people’s desserts.
(2004) and Chloe Moretz in the Swedish horror remake 
(2010).
A slew of actors were reported to be officially joining the cast of Ender’s Game today, with Harrison Ford being cast as Colonel Hyram Graff and Abigail Breslin as Ender’s sister Valentine Wiggin.