Grace, in a fit of madness, smothered her two children and then shot herself. She and the children are therefore stuck in their manor, never aging, never changing, just living each and every day knowing they are dead. Everything Grace knew about God and her religion, including the afterlife, has been destroyed by the absence of a life waiting for them beyond death. Charles was killed in the war and his wife and children may never see him again. Also, Grace truly loved her children despite her fit of madness and now has to spend the rest of her afterlife with the knowledge that she killed them and is responsible for their current predicament. Wow.
The scene where Charles returns from war also has the tendency to cause a few tears, as well as the scene where he leaves Grace the morning after they make love. It is the last time he's seen in the film. Heck, pretty much every scene with Charles counts as a tearjerker.