This page is for "lullaby", the song. See Lullaby (novel) for the Chuck Palahniuk novel.
A lullaby is a song sung to children before they go to sleep. The idea is that the song will lull the child to sleep.

One of the most famous lullabies, "Rock a bye baby", is hardly lulling. Although it starts mildly enough, it quickly turns to disaster:

Rock a bye baby, in the treetop
When the wind blows, the cradle will rock
When the bough breaks, the cradle will fall
And down will come baby, cradle, and all

Johannes Brahms wrote his famous "Lullaby" as a cradle song (Wiegenlied, in German), originally for a young singer whom he knew, Bertha Faber, on the occasion of the birth of her first child. The English lyrics are similar to the original German lyrics.

The lullaby generally known as "Mockingbird" makes many promises to the child if it will only be quiet and go to sleep, a sentiment with which parents will be familiar:

Hush little baby, don't say a word,
Momma's going to buy you a mockingbird

and goes on to promise "a looking glass", "a horse and coach", and other treasures. This song has had the unusual distinction of two separate manifestations as a popular song, first as the eponymous "Bo Diddley" and then, in a near-fugue arrangement, as "Mockingbird", a hit first for the brother-and-sister team, Inez and Charlie Fox, and then for then husband and wife James Taylor and Carly Simon, singing the Fox arrangement.