Watermelon, falling down

My family and I are having the usual evening lazy talk when my sister Gemma sang "Watermelon... watermelon" out of the blue. To our amazement, my nephew Emman continued the song and said, "falling down... falling down..."

Hahahah. Hilarious. We all laughed and Emman continued singing "falling down... falling down..."

You know why Emman sang that way?

My sister sang Watermelon in the tune of London Bridge. She said they have the same tune.

I have no idea =) LOL.