That had to have scared the daylights out of you and your wife... I'm so glad that things turned out as well as they did.
Discipline is a very touchy thing with some parents. An early bedtime is a fairly minimal penalty... and may not be enough to deter future aggressiveness. If the children may pose a threat to your daughter, by all means you do have to make sure she's safe, even if that means drastically limiting her contact with the boys. It's a shame that it has to affect a friendship, but her safety has to come first.