At the party just tell everyone what he said. It will be the entertainment.
Actually, although I would do just that, personally, I feel very sorry for their child indeed, and might, because really I'm a nice person, would go up to them in the playground and say, 'Th party is in a very nice place, and I promise to look after your dd and return her in one piece', and if they were still rude, I would just hate them forever