Facebook Messages have begun rolling out to everyone at a slow pace. If you never allowed them to have email before, they will soon. Facebook Messages gives everyone the ability to have an email address and a chosen username. If you have been limiting your kids from email all this time, it will be automatic for them according to Facebook.
They also handle the interaction differently. You are able to send and receive email just as messages would appear. This ability open them to communication outside of the walled garden of Facebook itself. There are steps you can take to limit the communication of this new email ability through privacy controls. We have a screencast and podcast (both from our sister sites TheSocialNetworker and TheSocialGeeks) does a quick walkthrough of the setup procedures and links to important help files.
The new privacy settings interested me more after reading them twice. You are able to set the level of who can email you based on everyone, friends of friends and just friends. that part fits the other models Facebook has implemented. However, friends are able to email you from any email address they register with Facebook. So this is a reverse privacy issue.
When you established your account with Facebook you provided a single email address. Most people only have one. Now Facebook is asking you to enter all of your possible email addresses so you could email in to any friend from any of them. This gives Facebook even more information on you as a person by associating email names, domains and possibly company names (if you use your company email) with your profile. People have not given this portion that much thought.
I would suggest you head out and quickly claim your name on Facebook, even if you do not use the email functions, ever. An example is my network page on Facebook. The URL would be http://www.facebook.com/IdoNotesNetwork (if you feel like becoming part, it is where I funnel all of my information on Facebook). So read the linked help files in the sister postings, watch the short screencast and get your Facebook Messages under control early.
You can see the entire screencast in HD on YouTube or embedded below.