Anybody who takes the word of a 5-year-old as confirmation of a family’s plans deserves what they get. It seems like the mom who wrote the bill did have an issue with the other family because she said this wasn’t the first party the other little boy missed after saying he would attend. Everybody involved could have handled this much better. The host family didn’t need to point out to their child which of his friends didn’t make the party. The other boy’s family should have let the host family know they couldn’t attend. I’m sure a parent of one of the boys’ classmates would know the name of the host mom, but it doesn’t sound like the 2nd mom made an attempt to find out how to contact her. Creating a bill and battling on FB was foolish and taking it to the press was worse. Some people just like drama.
No one is trying to compare the transgression of the no-show parent to a parent who abuses or neglects their child. Those two things are not even in the same universe, but it doesn’t make it any less rude or self centered to blow off a party that you’ve committed to. People do spend time and money on these things and I don’t believe the father when he says there was no way to get in touch.
That said, it is so awful that the birthday boys parents issued an invoice. Even putting aside the harm to the kids, there is no assumed obligation for the guest to pay. That’s the chance the hosts took when they booked an expensive children’s party that charges per person and requires payment in full 24 hours ahead of the event.
Hosting parents had every reason to be annoyed, but not to do what they did. No-show parents have a screw loose to publicize this whole mess.
When S was little I always had S’s birthday parties at home, something which was uncommon then and probably even more so now. And he has a November birthday, so they all had to be indoors. And through first grade, we routinely invited his whole class. (Luckily, I enjoy putting together themed decorations and treasure hunts and don’t mind cleaning up after toilet-paper mummies and the like. 
) So no-shows were not important at all. When he got a little older, we switched to a movie plus sleepover for a smaller group of friends. Again, no-shows not an issue. Thankfully.
If there is one thing I have learned as a party host is, expect no shows and also expect unexpected guests. You invite people for different reasons. Social and business obligations of course come to mind when planning an event. This is why I do not host parties where an exact head count matters. I would prefer that everyone feels welcome and no one feels guilty is something stops them from coming when expected.
I can’t imagine the thought of sending a bill to anyone for such a trivial amount of money. It is tacky and much more rude than anyone ditching out
I’m not sure I’d agree with that considering the beyond the pale tackiness and worse, threatening to bring a groundless legal suit against the child and parents.
Considering the outrageous behavior on the part of the host parents, they have no right to expect the very family they’ve not only treated rudely, but also attempted to threaten with legal action to protect them from the public shaming their behavior merits.
Kids parties in general have gotten out of hand with everyone trying to top the next person with entertainers, etc. Think about what kind of adults your kids will be.