The excerpt aired Tuesday on "Good Morning America." He also says seeing Bullock in the role of mother to 4 1/2-month-old son Louis is one of the "most amazing things" he's ever seen.
Says James: "She's like a fish to water. As soon as she put that baby in her hands, it was automatic and amazing."
The child was born in New Orleans, where the couple had spent time after Hurricane Katrina. Bullock has said she'll adopt as a single parent.