The zipper's the thing
I don't know why it should be that a zipper makes a bag so much more appealing to a kid, but it just does. My 10-year old daughter covets the zippered make-up bag I made for myself every time I pull it out of my non-zippered purse to put on some lipstick. I thought of her the second I saw Lisa Kingston's bags for kids in our Flickr pool--made out of her own Spoonflower printed fabric and with a zipper. She's got some for sale in her Etsy shop, too, if you're looking to buy handmade rather than making this holiday.