The young star plays an Asperger's sufferer who loses his father in the 2001 terrorist attacks on the Big Apple and director Stephen Daldry took him on a fact finding trip to New York for research.
Daldry tells WENN, "We spoke to a lot of different experts to help us out... We did all our 9/11 research which was fantastically eye-opening and wonderful. I took Thomas down to the tribute and the memorial and he went up to the Freedom Tower and he's written his name on one of the steel columns. It says, 'Thomas Horn'."
And the child star's doctor parents were a huge help as the director started making the film: "Thomas is blessed with both of his parents being doctors so we had quite a lot of access to knowledge and information and advice from his parents as well as from the individual experts that I brought in and spoke to about Asperger's."