I would ask. Any time a business could make a small accommodation that would help me, I will politely ask. If they say no, I will smile and say thank you anyway. If they say yes, I will thank them profusely. I think my kids can learn how to be gracious AND take care of themselves. To me, it is no different from asking to switch out a side item in a restaurant---I can ask nicely and accept whatever answer they give with grace. If I don't ask, they don't have the opportunity to help me. And really, the "free" bags are a marketing cost. They would rather my kid eat the candy and become loyal to it, that's why they give it away!