I started with Old Navy flip flops in pink & purple. A steal at $2.50 per pair.
I made the bows out of ribbon...a purple or pink polka dot bow and a "flip flop" printed ribbon bow on top.
The entire bow is held together with a thin ribbon tied through a button. And a bit of hot glue for reinforcement.
I glued the bows onto the flip flops with GOOP, and held them down with clips during drying. They seemed to be pretty firmly attached when they were dry.
We'll see how well they hold up to a group of dancing, twirling, partying 6 year olds!