Motherhood has been good to Julia Roberts: Since the birth of twins Phinnaeus Walter and Hazel Patricia on Nov. 28, "she's never been happier," says a friend. Still, Roberts isn't giving up the career that made her America's Sweetheart: She's completed work on a new movie version of the classic Charlotte's Web (as the voice of Charlotte) and she'll lend her pipes to the animated Ant Bully.