My Sister Momoko(2003)

Momoko, Kaeru no Uta ga Kikoeru yo

Momoko, who attends a special school, is both mentally and physically disabled. Every morning she becomes peevish because she can't go to the ordinary school with her twin brother Riki. Her family soothes Momoko by singing her favourite song "The Song of Frogs".

(Source: Eleven Arts)