In spite of my reference given above let me present another guess after looking into the standard Hebrew-German dictionaries of Wilhelm Gesenius and Ludwig Köhler:
The root D-A-H : to fly, to hover.
G. also has a reduplicated root D-D-H : to sway, and assumes that it is related to Arab. D-A'-D-A' : denoting a certin swaying movement [of the camel].
It could fit well to this song when percieved as a cradle song, and considering the flying away in the 3rd stanza.
But careful: it's only a guess.

Wilfried