The Irish actor, 50, appears alongside James, 23, in The Slightest Touch, which is scheduled for release on November 25.Â
The film follows Farrell and his friend Emma Fogarty, a disability rights activist, as they prepare for the Dublin Marathon, while also documenting the actor's experiences as a father to a young man with Angelman syndrome.
In a trailer for the documentary, Farrell acknowledges how unusual it is for him to allow filmmakers into his personal life.
"I've never had a camera crew come near my home," he said.
The Penguin star is then seen embracing James, sharing a lighthearted exchange that offers viewers a glimpse of their relationship.
"He gets away with nothing," Farrell joked.
James, whom Farrell shares with his former girlfriend Kim Bordenave, has Angelman syndrome, a rare genetic condition affecting speech, movement, balance and development.
The condition can cause significant communication difficulties and requires varying levels of lifelong support.
During a 2008 interview, Farrell spoke affectionately about his eldest child and the impact he had made on his life.
"He's nothing but a gift," he said.
"He's, as far as I'm concerned, exactly the way he should be."
He established the Colin Farrell Foundation in 2024, an organisation dedicated to supporting people with intellectual disabilities through advocacy, education and improved access to services.
The foundation focuses on the difficulties families can encounter when children with disabilities reach adulthood and lose access to educational programs and other forms of structured assistance.
"Once your child turns 21, they're kind of on their own," he told People.
"All the safeguards that are put in place, special ed classes, that all goes away, so you're left with a young adult who should be an integrated part of our modern society and more often than not is left behind."
The actor expressed his hopes for how James would be treated as he grew older.
"I want the world to treat him with kindness and respect."
The documentary also follows Fogarty, who lives with epidermolysis bullosa, a rare condition that causes the skin to become extremely fragile and vulnerable to blistering.
Her friendship with Farrell and their marathon preparations form another central part of the film, which examines the physical and emotional demands of their challenge.
