Aaron is a little boy with a slender figure, his father's dark blond hair, freckles, black eyes, a blue dinosaur shirt, gray sweatpants, white socks, and blue, green, and yellow velcro shoes.
Aaron is not considered a "normal son". His big sister describes him as a "smart, charming, dinosaur loving nerd", which fits him perfectly. He is obsessed with dinosaurs and has an overly-technical understanding of them.
He is a kid who fears being alone and admitting his own feelings. He is scared what will happen when his big sister leaves "the pack". He also backs out and leaves in very comical ways when he tried to talk to his crush, Abbey Posey. Katie helps build his confidence by giving him advice.
He has a very close relationship with his sister Katie and he becomes her voice of reason when it comes to strengthening her relationship with their father.
While it's never outright said in the movie, Aaron has shown signs of being autistic; missing social cues, having a strong understanding of a single area of interest, lack of friends, and has some habits like chewing on his fingers, shirt, or seatbelt when he is stressed or uncomfortable.
The Mitchells vs. the Machines
Katie Mitchell - There is no doubt that Katie and Aaron love each other deeply and are extremely close. Despite being siblings with a big age gap, they never once quarrel with each other. They have a playful handshake that they made up together called "The Raptor Bash". Near the beginning of the film, Aaron tells Katie that he is scared of being alone after she leaves for college. Katie immediately tells him that he will be okay and he will meet another "charming dinosaur loving nerd. (or lady nerd)". When Katie finds out about the family road trip, turns out Aaron was perfectly okay with this because he wanted to spend one last trip together with his big sister. Whenever Katie has a moment when she feels down, Aaron will usually be her voice of reason and will help her strengthen her relationship with their father, Rick Mitchell. Katie is the one that catches on that Aaron has a crush on their neighbor, Abbey Posey. She is extremely happy figuring this out and tells him to "don't hide from your feelings...that's no way to live."
Linda Mitchell - Linda, like Katie, is the parent Aaron is closer to. When Aaron gets captured by the robots, Linda goes full mama bear on the robots to get him back.
Rick Mitchell - Aaron's relationship with his dad is not nearly as complicated as it is with Rick and Katie, but its quick to tell he is not the parent he favors the most at first (especially when he tells him he might have to eat their dog, Monchi, for food). Rick does not think of Aaron as a normal, reasonable kid, but they still love each other nonetheless.
Monchi - Out of all the family members, Aaron is the most playful and closest with their dog.
Abbey Posey - Aaron's love interest. Abbey is always nice to him and they share the same interests but Aaron backs out in rather comical ways when he tries to talk to her. They are last seen hanging out and developing a close relationship near the end of the movie.