Your question is in the section of recipes and cakes, but I am answering the question as if it is really about baby diapers. You could wrap the baby in a couple paper towels....wrap them on like you would a diaper and then tape them to stay on. Then you could wrap the baby in something like Saran wrap, or even better...get a plastic food storage bag, cut leg holes at the bottom corners and slip the baby in. Paper towels to soak up the liquid and the plastic to keep it from leaking all over the place. I just wish I knew why you don't want your parents finding out.