None of that matters. As a minor, his is legally incapable of making his own decisions, including whether to play the Clarinet. His parents had a legal obligation to determine whether choosing to play the Clarinet was
1) safe for him, and that it would not cause him a permanent disabling injury
2) would not prevent him from pursuing his happiness by engaging in what they knew or should have known by his senior year in high school were his long-term career aspirations
Potential future income is always fair game in a civil trial.
If the child is still a minor, I would seriously consider involving Child Protective Services, since the parents have so obviously proved negligent in their duties of care.