We have made a little collection of fun embellished flip flops for the summer.
We embellished some interchangeable flip flops at our house with some simple flowers and some sticky velcro. Create whatever flower you would like and them place velcro on the back of the flower. Place the other side of the velcro on the flip flop. We have had good luck with the sticky back velcro but you could always reinforce it with some super glue or E6000 if needed.
Here area some other ideas that we loved.
Black ruffles with flowers at sWeeT cHarLi.
Crocheted with pink buttons at craft stylish.
A great tutorial for interchangeable flip flops at Makeit andloveit.
You may need this same solution at your house. I know that we do. Here is a "stay on strap" for the little feet around your house at Shannon Makes Stuff.