I hemmed all the way around the edge. I folded the material over twice so it had a nice, finished edge. Then, I strung a piece of yarn on a safety pin and guided it through the hem. I intend to replace the yarn with something better later.
The bag is so little. It's only about ten inches deep. It's not going to hold many Legos! It also does not open and close easily. I'm sure my four-year-old wouldn't be able to get it to lay flat in order to use it as a play mat.
My fifteen minutes was spent cleaning up from my project today. I'm back to the drawing board, too. I still like the idea of a Lego bag. I think if I can find a round table cloth, I'll put tabs around the edge for a drawstring. Maybe that will work. Any ideas?