To clarify -- was the older brother who dumped the glass the second time, after the cleanup, the brother of the child whose mother WAS home or the brother of the one where their parents were gone? Just wondered, because if it were the former, I would have gone back down to that mom and informed her (however late it was) that her other child had made things worse and retaliated. If it was the latter case, you can't do that.
The one parent did have her kid clean things up right away, which is good. I would try to maintain communications with her, maybe thank her for having her own kid clean up.
For the other family: Diane B. is right. Call the police department, or go there in person, and press for the police to send an officer in a marked car (that gets people's attention) to make a "friendly talk" visit, especially if this happened when there was no adult in town. It will be much more effective if you and your neighbor go ask for this together, so the police cannot dismiss this as just one grumpy neighbor doing a "those darned kids" routine.
I would ask the police to ensure that they do not identify which neighbors asked for a police visit. Yeah, the kids are going to know anyway, or at least have a good idea if there are numerous families they've ticked off over time. But I would still insist that no one be identified, and be sure the cops know about the retaliation.
Before you go, look up your state's regulations (it's usually in regulations rather than law) about the age at which kids can be left home alone. Ask the police to look into whether the kid(s) left home were actually all alone or were looked after by some adult you might not have seen, etc. Just having a cop ask the question could be enough to make those parents realize they could be in bigger trouble if they leave their kid(s) alone again.
Yes, get a security camera. Good point below that the camera itself could become a target for vandalism so choose with care. I would also keep a regular camera charged up and ready to grab easily if they start stuff like breaking thing in the street again -- take photos of it and if possible of them doing it, if your house's cameras won't catch it, but take any photos from inside your house so you aren't out there where the kids can throw stuff at YOU.
I don't know what else they've done but it sounds as if you have examples of other incidents since you characterize them as "bad kids" and are talking about security cameras--?
With summer coming, you'd better hope these kids have something to occupy them besides hanging out in the neighborhood.