What does the old man tell the children the reason for the battle was?

C

Explanation:

Remember, when the children; Wilhelmine and Peterkin where playing with an object they found, Peterkin asked the old man (Kaspar) what it was, he said it was a skull of a soldier who died in the battle.

Further asking about why the battle was fought, because he cannot remember, he said "The English routed the French, he says, in what later generations would call a great and famous victory".