If the students are going too hard on the beginners, the instructor either don't care or has lost control of the class. It's his or her responsibility to make sure everybody is safe. Most good schools ease their beginners into sparring. They start of with some light sparring, and then progress from there. Even pro fighters spar easy a lot of the time, as it's not worth the constant risk of injury or head trauma.
Now, this is a contact sport — bruises and a couple of cuts should be expected. Some times accidents happen, and you get injuries, such as broken nose or rib. However, if you are beaten to a pulp on a regular basis, this is most certainly a problem. You say nothing about the severity of the injuries, but still.
As for head gear, it's not a bad idea, but don't put too much faith into it. Depending on the style, it will protect you from some cuts, but you will still receive the blow. Keep that in mind, and keep your hands up. :)
Another important detail, is that there's no shame in telling your sparring partner to go lighter. If he or she can't submit to those terms (due to tournament preparations or other), he or she should find a more suitable partner. Even when sparring hard against an equal opponent, you should break in case of injury. This is common sense, as there is no reason to make the injury even worse. The fight can continue if the injured fighter feels okay, but keep in mind it's also important to treat injuries. Thanks to @Russell for pointing this out in the comments.