From the Hans Christian Andersen biography "The Life of Hans Christian Andersen. Day By Day", written by DPhil Johan de Mylius:
1812Encounters with the Theatre in Odense
In this year
HCA's father lets himself be conscripted as musketeer, in the place of a farmer's son, who thus pays to avoid military service. The amount his father received was probably approx. 1,000 rdl. (rix dollars), a large amount for the shoemaker. But with the bankruptcy of the state in January 1813, the money was devalued to 1/6 of its denomination, but only 1/10 of its actual value. As a result, the prospect of the money providing a secure future for the family simply evaporated.
HCA's earliest encounters with the real theatre commence in approx. 1812. Occasionally, he sees performances at Odense Theatre, for example during the first half of 1813 - Ferdinand Kauer's romantic, comic, magic opera (Zauberposse) Das Donauweibchen. HCA then attempts to act out the play at home, "- despite the fact that the only German words I knew were "Schwester" and "Bruder". - This play especially pleased me, in gibberish I created some German myself, wrapped my mother's scarf around my shoulders, and was now Knight Albrecht, then swimming on a stool like the girl from the Danube. All of these scenes did however frighten my mother, she forbade me to carry on like that, believing I must be mad".
(Levnedsbogen (The Biography))
This is HCA's first encounter with a mermaid and thereby his earliest source of inspiration for "The Little Mermaid".