Can we really call these individuals "kids" anymore? I'm assuming that all of the players are 18, or at the very least almost 18. They should be considered young adults(which is what they are) who are expected to act in a certain manner, with a certain level of maturity. Like someone said earlier, they are public figures, and should be held on higher standards than most college students. And I understand that they are still college students, and should be allowed to act as such, but to a certain extent.
Personally, I think its a shame that the coaching staff feels that they have to ban twitter. It almost shows a lack of trust by the staff...like they have to "babysit" the players to make sure they don't get into trouble. I would hope that the players would be aware enough to know what they should, or should not post.