James, who is Farrell's son with model Kim Bordenave, has Angelman Syndrome, a rare genetic disorder that is known to impair speech, movement and balance, reported People magazine.
Farrell says James is always reaching new milestones. "Every day, just breaking down boundaries.
"(James) is an absolute stud. He's an amazing boy," Farrell said at the premiere of his upcoming film 'Winter's Tale' in New York
Fatherhood was one of the main reasons the actor checked into rehab for drug and alcohol abuse in 2005.
"'Epic' (but) they didn't know it was me, so that was kind of a bummer. They seemed to think it was alright. I don't think it went to the top of their favorite list of cartoons, which is a bit disappointing," he said.
Farrell's latest film 'Winter's Tale' is set in a mythic New York City and spans more than a century.
The film releases in India tomorrow.
