Since we live in Florida, when my daughter wears shoes outside of school they are almost always flip flops. She puts a lot of wear and tear on them, so I wanted to go for a better quality pair this time. She put the Sanuks on and an hour later she said "Mom, these are the most comfortable flip flops ever! They feel nice and squishy under my feet." She is about to grow out of size 12, so we ordered the 12/13, and they fit just like I thought. They fit with a little room to grow. She said they felt a teensy bit tight at first, but clearly that changed once her feet sank down into the flip flops' cushy surface. (plus she was comparing them to the pair she'd nearly worn to shreds). While these don't have a defined arch, I think they do a good job for a flat flip flop. The yoga mat material has enough give to have the foot sink a bit into it while not squishing flat. Would definitely purchase the next size up when my girl grows out of these.