Terry, I dont think klonopin would be a good drug for your son. You dont want him on a drug like that long term. He is simply too young. Buspar maybe.
Seroquel does have some anti-anxiety help. It may be just the ticket. Before adding the extra lithium I would want to know how much he is on and get a lithium level. Can you take him to the hospital and do a blood draw for the level? His levels should be between 600 and 1000 I think but check the internet because its been a while since I did lithium levels. If he is too low or too high it could cause issues. Especially if its too high.