Smith was born in Elmhurst, Illinois. A Chicago-area hospital worker had approached the parents of young Smith about his auditioning for the leading role in a soon-to-be-filmed motion picture. Like Smith, the film's hero has Morquio Syndrome. The Smiths were concerned about exploitation but after reading the novel on which the film was based agreed to allow their son to audition. Although he eventually lost out on that role (the film was The Mighty and Kieran Culkin landed the part), Smith was recommended for another role in a film based on a novel. This time, his audition tape won over the director and the novice was hired to essay the title role of Simon Birch (1998), suggested by John Irving's A Prayer for Owen Meany. Because of his height, Smith was the perfect choice to play Simon, described as having been so small when he was born his mother didn't even notice the delivery. The novice actor proved a natural before the cameras and impressed some reviewers who found the film itself treacly and sentimental.