I don't generally know how much the parents pay for the birthday parties that my daughter goes to, so I would think that she doesn't know that you paid $27/child or that you had to pay for every individual child (Some places have you pay a lump sum for a certain number of children. She may think you might not have reached that limit). In any case, I think she is asking if her son can come without her paying. I would tell her that he is welcome to come, but that you already paid for everyone you were expecting, and she would have to pay the additional $27 for him. Surely, once she learns how much it is, she will not expect you to pay more. I bet the reason she is asking ahead of time (instead of just bringing her son) is because she does not know your arrangement with the bowling alley. Now that I think of it, I'm sure that what she really means by that text is, "I want to bring my son. How do I go about paying for him or do you have room in your package for another kid."