We all know the frustration and disappointment that comes when somebody eats the food we had our eye on. You go downstairs for that last serving of ice cream, only to find that your sibling has eaten it. In this case, it seems that Chela wanted to claim the cereal for herself, and she even left her parents a note informing them that they needed to ask her before eating any.
Sorry Chela, but the joke’s on you. Until you pay for your own groceries, there’s a good chance your parents won’t allow you to claim food as your own. That’s the stance her parents took by withdrawing the cost of the cereal from Chela’s piggybank. Well, she got what she wanted–she just hadn’t planned on paying for it.