The Atonement star and his actress wife Anne-Marie Duff welcomed baby Brendan last year (10), but remained tight-lipped about their new addition in a bid to keep him out of the spotlight.
Duff recently spoke more candidly about her son, revealing, ""He's just gorgeous... I do feel my life's completely expanded since he arrived"" - and now McAvoy has addressed how fatherhood has changed him.
He tells London's Evening Standard newspaper, ""I've become much more practical. And more efficient. But your world narrows, and the things you devote your new-found efficiency to are less. There are less things that you give a s**t about.""