McGrath said: I rather assume, given the etymological roots of pickaninny, in Spanish or Portuguese words that refer to children in general, that this would originally have been how it would have been used in English.

I think this assumption is incorrect. Sometimes what a word "should" mean, based on its etymology, is different from what it means in practical usage. If you insist on using words according to what they should mean rather than what they do mean, it's an impediment to communication at best, and an offensive one in this example. Pickaninny might not be a racial slur where you are, but it is in the US, and that's where Wesley S. is proposing to sing the song.

The other classic example I can think of right now is "anti-Semitic". Etymologically, this "should" mean being against all Semitic ethnic groups, including Arabs and Ethiopians. However, in real life this word is used and understood to mean prejudice against Jews. If a pedant uses it to mean prejudice against Arabs - because that's what it technically should include - this would be ineffective communication.

Marion