So after explaining this to my puzzled children I had them move out all of the chairs while I put a line of tape down the center of the room. Then I had them get in teams of 2, and then sent one person to each end of the room. (That way they'd have a friend to look at and I wouldn't have to count off.)
I had my 2 teams then on opposite sides. I had given my pianist a list of songs in the order I wanted him to play them (I put in a few silly songs too of course, nothing that needed to be sung too reverently because we don't want to mock Holy songs.) Then I told them that whoever sang the best and had the best dance moves while moving toward the line would be the winner of the rumble. It was hilarious! I wish I would have videoed their dance moves and their faces!!!
At first they moved to the line to quick and didn't really get into it. So I told them that to get the point to you couldn't get to the line before the song ended. And then they were crawling all over the floor, which isn't very appropriate for girls to do in dresses, so I had to make a rule against that. But all in all, this was one that the kids kept talking about and I got lots of happy questions about it from parents.