I would say no to those types of food and using food in general ....I guess you have to decide if the money they are paying you is worth the aggrevation and disruption in your day and the other children's day as this behaviour will run off on them. Do you NEED this family ? Can you make your bills with out them? Because I would tell the parents that this behaviour is unacceptable and you will not bribe her with food .... There are rules that all children must follow and if she can't follow them they need to source out new care. Give them a time line in which you need to see improvement.... And start advertising for a replacement !!!!!!