Welcome to HCM
We understand your concerns
I went through your problem description. I sincerely suggest that this might be due to the traumatic feeling associated with the accident and memories of the accident.
The doctors checked your son after and accident and they could not find much problems. Then your son might be fit. Then you should not worry about that part.
But do consult a psychologist
for further treatment. Children behavioral therapy
should give a good result.
Hope this answers your query. Available for further clarifications.