It's mind-boggling how hysterically sensitive some people are to every issue!
More to the point, though, "Pick a Bale" is among many children's albums and songbooks which show American culture through the ages. This song has been sung by many artists.
What I don't understand is this: The NAACP and others wish us to never forget slavery and its issues, yet the culture of the time(i.e. music and lyrics) must never been spoken.