Hi, first of all those quaks don't know what they are talking about, nerve conduction test can't test for the small fibre nerves, they are the ones responsible for the burning feeling, they should have done quanitive sensory testing for diagnosing obviuos small fibre damage, there is a better test as Bob mentioned called a skin punch biopsy but I don't think they do it here in Australia as far as I know.

If he can get his sugars into normal range [non diabetic range] he has a good chance of the nerves healing over time, I believe it's not only the high sugars but the low sugars also do damage to the nerves.
Supplements can also help the healing process, I swear by R - lipoic acic & GLA
[gamma-linolenic acid] at 480 mg daily, I also know other diabetic caused neuropathy patients which also say they feel much better by taking these supplements, the dosage for a child may differ so I would ask Mrs D about that.
I use to also take thiamine 100 mg x 3 times daily which did help the burning a bit as well, I never tried benfotiamine others here may be able to help you with that question.

Brian