Just pick up a ready made cake and have them write "Somewhere Over the Rainbow" with "Happy Birthday (your child's name) under it in the upper left or upper right. Then you can place the rainbow sugar shape on the opposit side.
You can then pick up a tube of yellow frosting and use it to make a "yellow brick road" from the bottom of your cake to the rainbow.
You can also pick up some tiny doll shoes, paint them red and put them on your "yellow brick road."
And remember to take a picture of your child's cake and to tell us all about your child's party with your free birthday web page.