Welcome to HCM!
I have gone through your query carefully and it doesn't have any symptoms apart from shoulders and neck pain
and that your son has low tolerance for pain, so, it is less likely that there is something serious about it ( no loss of consciousness
, which is an important sign for head injury
, or nausea
, vomit, dizziness
Shoulders and neck are sore because there are muscles and nerves which get injured during the accident. Manytimes, people dont remember at what places they are injured and only after few hours, one feels the pain at several sites and come to know of them.
Had I been at your place, I would wait for him to come back from school, and of there is increase in his pain, or there are certain fresh complaints , like: nausea, vomiting
, vision difficulties, dizziness ect., I would certainly go and see a doctor.
If the pain is decreasing and he is otherwise absolutely normal, you can just wait.
----If the anxiety
for his health is taking over you, getting an MRI Brain will clear the picture at once!
Hope the answer helps you
Feel free to ask more questions