Are you using what they call a tom Thumb? Does it have a snaffle mouthpiece and shanks? If so, I would immediately put him in a ring snaffle, eggbutt or d ring, but a regular snaffle without any shanks at all. Any type of shank on a baby will cause problems
As far as chewing, thats pretty normal for a youngster, they chew and mess with the bit until they get used to it. He will get used to it, but he needs to learn that a bit is okay. Put it in his mouth on a headstall, let him walk around his stall or corral with it in his mouth(be there to watch him) and let him figure it out, find out its not a bad thing, it won't hurt him and he will get used to it.