What outrageously bad behaviour. I too would take steps to make sure this never happens again. No need to rant, but a quiet sit down with your fella and the parents (without the children in earshot) where you can state your case and lay down some rules for the next visit is definitely in order.
If they are doing this at your place (and so young too), what the heck are they up to when they are out in public? I'm with gramqlts and many others...not enough wooden spoons being waved about these days!