I have made several diaper bags for others. I found a pattern on all free sewing that works well. I put pockets on the outside and the inside. A zipper on the top and handles that can go around the shouldar or the neck to make it easier to handle with baby in tow.
http://www.allfreesewing.com/Sewing-...g-pattern/ct/1 Here is the basic pattern that I started with and I vary it according to the needs of the mother to be.