Egyptian straw flip-flops (Vatican Museum, Rome)
Many people in ancient Egypt went barefoot their whole lives. It was warm there even in the winter, and people thought shoes were an unnecessary expense. Kids, especially, didn't usually have any shoes.
Children's sandals from New Kingdom Thebes (Vatican Museum, Rome)
Most people who did have shoes wore shoes made out of straw or reeds. Shoemakers took the straw or reeds and wove it into flip-flops that you could buy at the shoe store. (The ones in the pictures are missing the top cords, which have broken or gotten lost, just like the ones on your flip-flops do.)
Here's a video that shows a man weaving Japanese straw sandals:
The earliest known version of the Cinderella story involves an Egyptian slave girl who loses her straw slipper. Her straw slipper shows that she's poor, like our Cinderella. Rich people didn't wear straw sandals. They had sandals made out of leather, which were stronger and lasted longer.
To find out more about ancient Egyptian clothing, check out these books from Amazon.com or from your library:
Eyewitness: Ancient Egypt, by George Hart. For kids.
Ancient Egyptian Fashions, by Tom Tierney (1999). For kids.
Ancient Egyptian Costumes Paper Dolls, by Tom Tierney (1997).
Women's Work: The First 20,000 Years : Women, Cloth, and Society in Early Times, by Elizabeth Wayland Barber (1995). Not for kids, but an interested high schooler could read it. Fascinating ideas about the way people made cloth in ancient times, and why it was that way.