"Who's the Leader" is a fun game described on page 16 of the November 2003 issue of The Friend. I think it could be adapted to singing time by adding a review song(s) to the actions the children are doing.
Play the game by gathering into a circle. Send a child from the room. Choose another child to be the leader and have them choose actions like marching in place, waving a hand, patting their head, etc. They'll need to have several in mind and change them during the round of play. The rest of the children follow the leader's actions. Begin singing a review song and invite the first child back into the room. This child stands in the circle and tries to discover who the leader is by watching the children follow him. After the discovery is made you can repeat the game with two more children as often as interest or time allows.
The game fits perfectly with our theme in March and would be a good game to use to review the song "Follow the Prophet" (CS-110).