You can use any shape. It doesn't have to be a bunny. Just trace a shape or cookie cutter. This would be cute for any holiday, just use an appropriate cookie cutter to trace and cut out the shape, then whatever yarn works best for that holiday!
Homemade Bath Crayons from Little Crunchy Mama: Buy some glycerin soap at a craft store. Melt it in the microwave, add food coloring, and pour into an ice cube tray. Takes about an hour to cool completely, then pop out of the mold and you have crayons!