In this post we have lots of free PDFs for this song, including melody, chords, fingerpicking and fingerstyle. You can find more like this in my ebook Easy Songs in the Public Domain for Fingerstyle Ukulele.
Fingerstyle Ukulele Arrangement
Simple Melody and Chords Arrangements
These melody arrangements should also work for Violin, Sax, Clarinet and Flute.
Violin_Twinkle Twinkle Little Star
Alto Sax_Twinkle Twinkle Little Star
Clarinet_Twinkle Twinkle Little Star
Flute_Twinkle Twinkle Little Star