"With my son the only time I'm reminded that there is something different about him - that he has some deviation of what is perceived to be normal - is when I see him with other four-year-olds. Then I go, 'Oh yeah', and it comes back to me," the Mirror quoted him, as saying.
"But from day one I felt that he's the way he's meant to be," he added.
However, Farrell, who has joint custody of James with his model mother Kim Bordenave, said that he is determined to help his child grow up to be happy.
"I think it's like any parent. What I want to do for my son is just to make sure that he has the opportunity to reach his individual potential," he said.
"And that he's happy as can be. And I'll do whatever I can do, stay in his way, get out of his way, to see that that's realised. That's what it's all about," he added.