I thought of something...
I was listening to my 5 year old say "Nah nah-nah nah nah nah! You can't catch me!"
I remember saying the same thing when I was 5 years old. I probably heard it from my friends. But I did not teach this to my son. I'm pretty sure that his daycare teacher did not teach him this. I don't think he saw it on TV.
So this means that he learned it from his peers, and that the saying "nah nah-nah nah nah" must be passed down through generations of 5 year olds.
Very interesting...