Frère
Jacques is a classic in the French original version and its melody has
been used an re-used in many nursery rhymes worldwide.
There are many - often contradicting - theories about the origin of the
song.
Often the original version is linked to a famous 'Jacques', Jacques
de Molay of the Knights Templar in France.
In any case it's a simple and well-recognised song, making it well
suited as a lullaby.