The (low-level) PCs come upon a large battlefield. The wolves and ravens have come to feast on the dead; there appear to be no survivors at all. Yes, OK, they can loot, but the loot is just used weapons and armor.

As they turn to leave, they see, hidden away from the battlefield, a small child, scared and crying, who says, "Have you seen my daddy?"

He has no clothes except a wool blanket, which gives no clues whatsoever.

The child has no name for his father except "Daddy", and can provide no useful information. He is just a difficult problem for them as long as he's with them.

Presumably, they will find some kind of foster-parents.

Several adventures later, when it is impossible to re-find him, they will hear about the kingdom that has plunged into anarchy because the heir to the throne was lost in a great battle.