The reason is that the Americans didn't know that war was officially over and that the peace treaty was already signed. The peace was signed in December of 1814, while the battle happened in January of 1815.
Explanation:
We need to have in mind that in this information people still needed a lot of time to obtain certain information from different continent. Literally, you needed someone to transmit information by boat, and it usually needed a couple of months for it. It is interesting that Americans believed that this battle was decisive one.
As a parent, you should tell them there isn't anything under the bed. If they are still complaining, then comfort them and show them the truth that there are no monsters under the bed whatsoever.
