This page says it's in "Walton's New Treasury of Irish Songs and Ballads."

This version is sung by Máiréad Ní Mhaonaigh on the album "Seal Maiden: A Celtic Musical," by Karan Casey & Friends, 2000:

THE CRADLE SONG

Sweet babe, a golden cradle holds thee.
Soft a snow-white fleece enfolds thee.
Fairest flower all strewn before thee.
Birds warble o'er thee.
Seoithín seo ló, seoithín seo lú la ló.

Oh, who is this a-lying here
Gently at the door of my heart?
To and fro like clouds at night,
I softly rock your cradle.
Seoithín seo ló, seoithín seo lú la ló

A yellow moon lies in the sky,
Streaming, falling over the earth.
Hush, a leanna, hush, be still.
The world is silent and sleeping.
Seoithín seo ló, seoithín seo lú la ló.