"Dormi Jesu" is a beautiful little Latin lullaby that was copied by the English poet Samuel Taylor Coleridge from a print that he saw in a German village, and which he then published in Sibylline Leaves in 1817.
The Hymns and Carols of Christmas website provides the Latin text along with Coleridge's English version, "The Virgin's Cradle-Hymn." The CPDL website has MIDI files, sheet music, and an English translation, and the Canasg Music website also provides a MIDI file for you to listen to, along with an English translation.
Notice the wonderful use of the diminutives blandule and somnule here in the Latin, perfect for the lullaby theme.
Dormi, Jesu! Mater ridet,
quae tam dulcem somnum videt,
Dormi, Jesu blandule!
Si non dormis, mater plorat.
Inter fila cantans orat:
Blande veni somnule!