This is a really easy sewing project. Even a beginner to make this happen!
Here are two edges that you can have. I have a serger and I use that bad boy every chance I can. I had a defective one (which i returned and got a better one!) so I was able to test out two different ways to make this! You can serge that velcro right to the top of the bag without needing to hem it or you can zig zag stitch it and zig zag up the sides! Basically just fold it in half and sew up the sides! This fabric I used it called PUL (polyurethane) I bought it at joanns in the Baby Boutique section - it is marketed to be used as reusable diaper covers. If you can find this you can also use oil cloth.
Just showing you it's waterproof!
Here is my 2 year old eating some craisins out of one.