Sarah Polley doesn’t need a baby sitter. The new mom brought her tiny daughter to Sons of Essex for the Peggy Siegal Company and Forevermark party for her film “Take This Waltz” on Thursday night. The petite actress and director took time to breast- feed under a blanket at a back corner table before greeting guests while rocking the infant in her arms. “I’m trying to not talk about her and pretend she’s not here. I know it’s hard to not talk about her when she’s on me,” she told us.