>> Nanny nanny boo boo? LOL! What's that?
http://duckduckgo.com/?q=nanny+nanny+boo+boo&t=vivaldi&ia=web
It was following the 'childrens' mini-meme ...
Children love to say "I know something you don't !"
So, nanny nanny boo boo is a return taunt that children issue. I didn't think it was a 'Southern thang', but some of the sources say it is.
When the children are mad at someone, the taunt is extended with '... stick your face in doo doo'.
I had forgotten about that part until you asked me 'What's that'.