Okay, I love this line, so I remembered. Forgotten little film with Leslie Caron and Warren Beatty called Promise Her Anything, from I think 1965. It's New York, they're neighbors. He makes lightweight porn for a living, she's a widow or divorcee with a toddler. She's decided to look for the perfect husband, which she decides is, of all people, Robert Cummings, her boss and a baby shrink who can't stand kids. Not a great film, but I love, love that moment and that line when they're moving in and the kid wanders into his bedroom and calls him Daddy. I deny everything and demand proof!