Both of my littles liked the Merry Widow Waltz, hummed slowly. Someone has a nice birthday quatrain to the melody, too:"Happy birthday, happy birthday, we love you/Happy birthday, and may all your dreams come true/When you blow out the candles, one remains aglow/It's the lovelight in your heart where'e'er you go. " I, personally, have never been able to work this into a kids' birthday party, since they can be a tad obsessive about ritual, but it's fun to sing.