1917. Although the autograph manuscript is titled "Sonatine," the first edition, published in 1928 by the Japan Symphony Association Publishing Department, was released as "Kodomo no Sonata" (Children's Sonata). It is said to have been written for Yamada's children, and the composer's preface to this first edition states: "It is the wish of the composer, as a father, that children, from an early age, encounter the correct forms of music and deeply appreciate the content that flows within those forms—the story of sounds, detached from words—that has become this short piece."

• First Movement: B-flat major, Allegretto
• Second Movement: E-flat major, Andante
• Third Movement: B-flat major, Petit Rondo

Additionally, among Kosaku Yamada's sonatinas, there are "Two Sonatinas" which existed only as autograph manuscripts and printing plates and were not published until recently. (Published in 2022 by Muse Press in Kosaku Yamada: Piano Works Miscellany Vol. 1 'Early Works in Classical Style').