I have to agree with having someone else give him lessons and build his confidence. It has nothing to do with your ability and everything to do with your mother/son relationship Kids tend to do better when anyone but their parent is coaching them.
It is not uncommon in the large horse world to simply pay a trainer (usually your own) but not always to find exactly what you are looking for. You have to pay a finders fee however that usually allows you to have access to many more horses as well as free trials and a whole network of clients...