I've had a miscarriage, and there was nothing "fortunate" about that. It was painful, bloody and messy, and I was mourning the loss of the potential life.
Did you forget to have The Talk with your daughter, or what? How did she manage to get pregnant twice in four years? Sure, you can have the misfortune of malfunctioning birth-controls, but that's not what happened here, is it, Daddy?
Besides, women who get pregnant before their bodies are ready to actually, ya know, carry and give birth, are more susceptible to miscarriages and still-born children. You should protect yourself and your partner, both from unwanted pregnancies and from STD:s, especially when you are both too young to be a parent.