What object does Gabe give Diana in Act 2, Scene 8? What song is sung?

Diana is handed the music box by Gabe. She listens to it, and Gabe hums along with its song. Dan interrupts, and Diana starts remembering how the music box helped their son sleep. Music starts ("How Could I Ever Forget?", a careful, slow, ballad) as Diana remembers the details of Gabe's death and rushing him to the hospital when he was only a few months old.