To make visual:
Draw a large birthday cake on the posterboard. You could also use colored paper and cut out the shapes for a cake. Decorate with "icing" and whatever embelleshments you please. Don't draw any candles on the cake, though! I think this will work better in a landscape format. Laminate the poster, or cover with contact paper.
For the art, print out the candles for each verse. You can place the candles on the cake poster, or have helpers do this for you. As you learn the song, have helpers come up and "blow out" the candles on the cake - they can remove any of them they want. Since there are 12 candles, you can also put names in a hat, and the child that has their name drawn can take off as many candles as they are old. For example, a 7-year-old child would remove 7 of the candles. This would also be a fun one to have the birthday kids for the week help out with.
Verse 1:
Get a picture of Christ being baptized from
the meetinghouse library