The film, out on Friday, is based on the bestselling novel of the same name by R J Palacio, and follows Auggie's journey as he takes the difficult step of his first year at school.
"For me, when I read the book, I thought it was so special, so incredible the way she had crafted the story about this family, and that's really a story about all of us," says Roberts.
Roberts's character, Isabel Pullman, home educates Auggie - played by 11-year-old Jacob Tremblay - until he is 10 before deciding to send him to school.