One thing Liv Tyler has noticed about being a mom: "What they say about your brain cells going out the window when you have a baby is so true," she says. "You get really flighty." Still, Tyler (in New York City on Aug. 1) wouldn't trade having son Milo, born Dec. 14, 2004, for anything. "You are so in love with your baby that when you go out, you're like, 'Oh, I miss him!' "