Hello,
Thanks for posting your query in HCM,
If your son has had a wrist dislocation, his symptoms would be extensive pain, quite a lot of swelling, restriction of movements in the affected hand. From the description that you have provided, it does not seem like a wrist dislocation, moreover, it should be a 
sprain. 
I would suggest you to do the following measures:
- immobilize the affected wrist with a wooden 
splint, so that any movements may not cause any further pain
- Do not 
massage over the area
- yo may also consider attaching the splint with a neck sling for the comfort of the child
You are required to consult with a doctor or go to an ER for proper examination and management.
Hope this helps
Kindly revert back for any further queries you have.
Thanks and regards