Childs horse...Trainers & the like please...?

This poor guy has really been abused. Not meant as a criticism but did you not ever check on him to make sure he was OK. It's irrelevant now, but how sad he has come to this. Regardless of how people appear, so many know nothing about horses. Sorry to hear this happened to him. Too bad you are unable to help him now. Sounds like he needs a total re-start from the very basic level in order to get him to accept a rider and not be so nervous. The chewing on the bit indicates he is so nervous and fearful. He is just waiting for the "next attack". I wouldn't over-stress him or try to hurry the process of reindoctrinating him. Let him relax. Sometimes re-starting a horse is much more difficult than starting a green horse. Take care and good luck to you.