a pregnant and expecting yukkuri sunbaths *to let the babies thrive*, and sings what could be considered songs - the entire day
yu~ grow up easy~
yu~yu~ babies, bathe easy~ (lit. be covered)
note: "bokko shi nagara" - not entirely sure about that part, but pretty sure it's related to giving the babies good fortune or letting them prosper/thrive, or something similar. again, not the best literal translating, but the gist of it is there