Here is an Advent Song that we sing everyday when we light the candles. I don't know where I originally found this, but it is great for little ones.
It is song to the tune of twinkle twinkle little star.
Advent is a time to wait.
Not quite time to celebrate.
Light the candles one by one.
Till the Advent time is done.
Christmas day will soon be here.
Time for joy and time for cheer.