Irrespective of age, we mourn for those loved and lost. Mourning is one of the deepest expressions of pure love. It is a natural response in complete accord with divine commandment: “Thou shalt live together in love, insomuch that thou shalt weep for the loss of them that die.” (D&C 42:45.)
Moreover, we can’t fully appreciate joyful reunions later without tearful separations now. The only way to take sorrow out of death is to take love out of life.