This game is great for last minute subs, change of plans, etc, and it forces the kids to review the program songs without realizing that they're working!
Make a list of the songs you'd like to review and give it to the pianist. Be sure to throw some fun songs in.
Split the children into two groups. Pick a child from the first group to roll a die. The number that is rolled represents the number of notes that the pianist will play. Choose another child from the group to guess the name of the song. If the child guesses correctly, the first group gets one point. If the guess is incorrect, the second group gets a turn.
The pianist plays the clue again, adding one additional note. Play continues back and forth until one team guesses correctly. Once the name of the song has been guessed, the whole primary sings. Then team two gets to roll the die.
When playing games, remember that we are counseled not to encourage excessive competition. If you sense that the children are getting too competitive, discontinue play and transition into another activity. If at all possible, I like to end the game on a tie. Be sure to congratulate both teams on their knowledge, singing ability, teamwork, etc. and stress that THIS is what is important.
As an alternative, you may have the pianist choose the songs and play adults versus children!