Yes, Facebook can be used for bullying and yes Facebook can be used by paeodophiles to "groom" children. All that can happen in real life too in situations where you might think it entirely appropriate for children to be.
Let' get some perspective here. If as a parent you responsibly monitor your children's use of Facebook then you or they shouldn't encounter problems.
As for reporting under age members to Facebook, do you honestly think that the powers that be at Facebook really give a flying fuck about kids being on there? Get real. It's bit like drugs in prisons. Everyone knows they shouldn't be there but equally everyone knows drug use is absolutely rife in prisons. A blind eye is turned to it because it suits the powers that to not do otherwise.
Facebook is absolutely choc full of underage profiles. A brief perusal of the site bears that out. The powers that be at Facebook are just as aware of that fact as we all are. I'm sure that they'd delete a profile on request, just to placate someone, but the vast majority of people aren't remotely bothered by children being there and even positivly encourage it so I expect they get few complaints off adults. Most parents I know have no issues whatsoever with their children having Facebook accounts. They monitor them sensibly and responsibly and the chidren get fun out of them.
All that the powers that be at Facebook are interested in is the success of Facebook and that is assured by making it as popular as possible and used by as many people as possible.
So save your time and energy and spare us your righteous indignation. If you're really that bothered about only being able to correspond with adult friends exclusively then I suggest you deny the friend requests of any children who try to add you, or if you don't feel you can do that (probably because your principles go out of the window when you're worried you might offend your friends if you reject their little Suzie or Johnny's friend requests) simply stick to e mailing your friends privately, speaking to them on MSN or 'phoning them.