As already said, if they're usually quiet turn a deaf ear. You've got an extra hour in bed tonight and there is no school tomorrow in any case.
Next time you bump in to them, ask them to let you know when they are having a party/making an evening of it, so you can prepare.
But as you say the youngest are sleeping I don't see there is a problem.
If you know your neighbours are having a late, loud night take the opportunity to make it a fun night for your family. Watch films together, or play Wii, have a buffet supper, assuming it isn't a school night.
One day your eldest will be old enough to want a late party.