Some people claim that this song was created by a pilgrim boy who sailed to America on the Mayflower. There he saw cradles made out of birch bark hanging from the trees. That's how some of the Indians made them in those days.

Rock-a-bye baby
On the tree top,
When the wind blows
The cradle will rock,
When the bough breaks
The cradle will fall and
Down will come baby,
Cradle and all.
Notes
Below is a version of Rock-a-bye Baby that I found in A History of Nursery Rhymes (1899) by Percy B. Green...
Hush-a-by, baby, on a green bock (Saxon for bough);
When the wind blows the cradle will rock.
Here's the version from A Book for Bairns and Big Folk, Children's Rhymes, Games, Songs, and Stories (1904), by Robert Ford:
Hush-a-by Baby on the Tree Top
Hush-a-by baby on the tree top,
When the wind blows the cradle will rock;
When the bough breaks the cradle will fall,
And down will come cradle and baby and all.
Ford wrote, "This is a rhyme which 'every child has joyed to hear.' Its origin, as told in the records of the Boston (U.S.) Historical Society, is not more curious than beautiful and significant. 'Shortly after our forefathers landed at Plymouth, Massachusetts (I am quoting), a party were out in the fields where the Indian women were picking strawberries. Several of the women, or squaws as they were called, had papooses - that is babies - and, having no cradle, they had them tied up in Indian fashion and hung from the limbs of the surrounding trees. Sure enough, when the wind blew these cradles would rock! A young man of the party observing this, pulled off a piece of bark and wrote off the above words, which is believed to be the first poetry written in America.'"
Photos & Illustrations

Comments
See Hush-a-bye Baby for a less scary version.
Thanks and Acknowledgements
The first illustration is by Jessie Willcox Smith (1912) and the second is from The Real Mother Goose (1916), illustrated by Blanche Fisher Wright. The score and tune come from A Baby's Opera (circa 1877), by Walter Crane.
Many thanks to Jason Pomerantz for singing Rock-a-bye Baby for Mama Lisa's World!
2nd recording by Ruth Golding.













