For my daughter Payton's 5th Birthday, we bought plain straw hats at our local discount store and lots of different plastic flowers, ribbons, etc.  The girls got to pick out which flowers ext. they wanted and showed us where to hot glue them on their hat. They loved it. We got pictures of all the girls in their hats with a digital camera and printed them off so when they went home their folks could see the fun they had.  They also kept the hats!    My daughters Birthday cake was also a sunbonnet cake. It was lots of fun and entertaining.