Dreft detergent is used for baby clothes because it is supposedly a gentle detergent and it smells nice. It won't make a difference in washing allergens out of a quilts. I would think that machine washing with any detergent and then machine drying should work just as well. Then place it directly from the dryer into a plastic sealable bag and take it out of the house. You will have to let the parents decide if they think that is sufficient. Just describe to them what you did. I hope it works for your grandchild and you! It will probably depend on the severity of the allergy.