Mr. Leisinger said in a telephone interview that the pieces were probably composed in 1763 or 1764, when Mozart was 7 or 8. If truly by him, they would serve as an important link between his simple earliest compositions and his first major works, Mr. Leisinger said.

Image The scores attributed to Mozart, in his fathers handwriting. Credit... Mike Vogl/European Pressphoto Agency

Neal Zaslaw, a Cornell University music professor and Mozart expert who was not involved in the discovery, said the attribution to young Wolfgang was “highly plausible,” although it was not likely that it could be proved “beyond a reasonable doubt.”

Called “Nannerl’s Music Book,” the manuscript volume containing the pieces has long been known and studied. It has been in the Mozarteum since 1864. Mr. Leisinger said that preparation of a facsimile edition by the Mozarteum prompted him to examine the pieces more closely and ultimately led to his deduction. He said that the concerto part and the prelude were musically and technically related.

Leopold used the music notebook to give Nannerl, as his daughter Maria Anna was called, keyboard lessons. It contains some 60 pieces, many by contemporary composers and 18 recognized as by Mozart. Most of those are in Leopold’s handwriting, composed before Wolfgang had a firm grasp of writing out music, Mr. Leisinger said. After Mozart’s death, Nannerl ripped out pages with his handwriting and gave them away to friends and Mozart admirers.

The two newly examined pieces were written hastily, with corrections, evidence that Leopold was not copying out somebody else’s work. At the same time the nature of the music departs from the compositions Leopold himself was producing. Instead the concerto movement, labeled Molto Allegro, contains a multitude of notes and technically demanding, sometimes awkward, passages.