If they had caused physical damage than yes... If they made the victim commit suicide than yes.... Although peoples opinions differ, just verbal/mental abuse can't really be treated as a crime.... Although I do not agree with this, that is how it is...
If the bully lead to the victim to self harm, then maybe not be treated as a criminal, but have stricter punishments. Schools do nothing about it when they should. Do I think they should go to jail? No. Bullies are just insecure people who like to make others feel bad. Being treated as a criminal will not really do anything.
Bullying is a natural animal behavior to establish dominance. Humans have been doing it for thousands of years. In polite civilized society, for the last couple of hundred years it has been frowned upon, and checked when ever possible.
No. Bullies should be helped through their own problems, because every bully has a bully. Don't believe me? Hitler. He wasn't hateful just because he was a big turd. He had his own reasons. Am I justifying what he did? NO. Not in any world would I do that. Back to the subject... Bullies should not be treated as criminals. Criminals should be treated as criminals. While their actions are detestable and unnecessary, if a child or teen is bullying, they should be given counseling and be presented with positive actions and help. Punish for what they do, not for what they suffer for. How crappy is it to always have everyone treat you like a criminal? Eventually you start to believe you are one and then guess what happens? If someone does wrong, punish the wrong. Don't treat someone like a piece of crap.