I also have not vaccinated *any* of mine against the CP. And I *DO* hope they get it naturally!
I *might* go so far as to attend a CP party, but I've never had the real life opportunity.
BUT...I would have to first research the risk to my mom, who lives with us, has MS, and might end up w/shingles. If that was a high possibility, I would NOT INTENTIONALLY expose my child to CP. (it just occured to me right now that this would be a consideration actually, thanks to a comment or two I read.)
And I would not INTENTIONALLY expose my kids during the time I had a newborn in the house.
Yes, they *could* get it anyway. That's beyond my control. And no, I'm not planning to vax them for it because I don't believe it *will* prevent it. I have a friend whose 3 kids were *all* vax'ed at least one shot against the CP, I think the oldest was in school and had had the 2 recommended. They *all* got the CP and the oldest actually got it the *worst.* (she didn't live close enough or i might have gone ahead and exposed mine then )
Me, in your situation, I would have told my friend about the exposure and the chance of them being contagious at the party (next to zero apparently) in a way that gives her the option of backing out nicely like "Hey, my kids were exposed to CP, it will have been 6 days by the time of your party, they should not be contagious until at least 10 days...but are you OK with them still coming?" or something like that.
Even if I were thinking of going to a gathering with mainly non-vaxers, I know quite a few....I would still inform them if my kids had been exposed to something and let them make the decision. After all, they are the only ones who know if they're, say, going to be around a newborn or someone who has a weakened immune system. Or going to visit Grandma for Christmas next week or whatever.
And *I* as hostess of a party, would have done the same thing your friend did, though I would have said it much nicer like "*I* personally know the risk of spreading this is pretty low at this point, but this is not a good time for me to intentionally expose my kids , and I can't speak for everyone at my party, I don't know all their situations....I just can't risk even a small chance of exposing everyone."
I also would not bring my children to a gathering after they'd been exposed to CP (and I knew of the exposure) unless it was an agreed-upon intentional CP party. (or insert other "preventable by vax" disease here) I would never want to be responsible for indirectly exposing someone's immune-compromised or newborn family member, etc.
Just a responsibility I accept.