There is no word for feeling nostalgic about the future, but that's what a parent's tears often are, a nostalgia for something that has not yet occurred. They are the pain of hope, the helplessness of hope, and finally, the surrender to hope.
You're Not Doing It Right: Tales of Marriage, Sex, Death, and Other Humiliations (ed. Simon and Schuster, 2012) - ISBN: 9781439167953