Twinkle, Twinkle Little Star and the Alphabet song have the same melody
Although this fact is quiet obvious, it is rarely noticed. The melody for both of these songs actually derives from French song "Ah! vous dirai-je, Maman" and has inspired many great composers throughout 18th - 20th century.
Because of the simplicity of this melody, multiple variations of songs using the melody of "Ah! vous dirai-je, Maman" are known all around the world including "Twinkle, Twinkle Litle Star", "Alphabet Song", "Baa, Baa, Black Sheep", "Morgen kommt der Weihnachtsmann" and others.