What would you do in this situation?

i would feel as upset as you do if this happened to me. since the owner's clearly don't care, i would make a point to spread this news via word of mouth. you could write a ltter to the paper but they often won't print specific business names. you could also try writing a letter to the owner's telling them you won't be booking a party you planned on having there (make it much larger than the kid's one) and will be telling all your guests exactly why. include that as a regular bowler, will never be back to their establishment. say that while you understood there was a party, it was their ATTITUDE and UNWILLINGNESS to help with your problem that made you so upset. put the blame on them, not the kids or parents.