Music (I vote for kids music, or whatever you feel is appropriate for their age)
Music Player (iPod/iPad, DVD player, CD player, Computer/tablet (for using Pandora), etc.
Your Voice (in case the power is out and you want to create music anyway)
Here's how it went:
I turned on the music and the girls just started dancing!
This activity was a lot of fun. And adults can do it too if they want. Mostly the girls just stomped their feet, twirled, and jumped with their arms in the air.