Wow - steeping not sleeping - never noticed either - see the RUS thread.
But, since the song is originally Welsh, wouldn't be better to sing the original lyrics or a translation?
There's a translation of the original Welsh at
This too says steeping!! But the original song was not a lullaby, but about old age.
I hope that some may like the translation well enough to sing that or there is another web site that has a phonetic translation of the Welsh - or Cymdeithas Madog has recently released a cd of readings and slow singing of Welsh folk song lyrics, including this song.
Hwyl, Chris yn Wheaton