Yeah I'm with you, AH013, although I have yet to see an article that explains the situation in a way that makes sense. I suspect the hostess might be nuts and terrible at communication, but in the abstract this seems like if you told a friend you'd go to the movies with them so they reserved and paid for a ticket for you and now you're saying you shouldn't have to pay them back because you didn't show up.
And actually if the case was that she would have paid for them coming if they'd come, that makes me even more sympathetic towards her. She was happy to treat them and wouldn't have minded spending the money in that case.
24 bucks isn't much, but that means if four kids are no-shows you're out almost 100 bucks for nothing. Granted, if you can't handle that you could choose a less expensive option for your kid's party, but whether you can afford it or not doesn't affect whether it's rude.
It doesn't help that this article features a picture of the dad, which, I know Americans characteristically don't dress well*, but his deliberately scruffy stubble beard, hip glasses, and deliberate bed-head make me want to punch him in the face. And while the hostess's attitudes might be questionable, I can't stand the whiny 'How dare you pass a note to us through our son!!' weirdness. Like, really? Aside from the weird sanctity-of-the-child argument, it seems contradictory to argue that you had no possible way of contacting with the hostess (so there obviously isn't a contact list or an established system for parent-to-parent communication) but you're mad at her for using the only possible path of communication as though she had an alternative.
*edit to clarify: even though it's common to be more fashionable in his country than in mine, his emphasis on looking cool and hip pisses me off