Hi, thanks for using healthcare magic
It is understandable to be worried.
If he is behaving normally then it is likely that he is ok.
Signs or symptoms of brain injury
at his age would be unusual drowsiness
, irritability , vomiting, loss of consciousness
and drainage of fluid from the nose, mouth or ears.
You may want to apply a cold compress to the area that was struck to reduce any potential swelling.
You can monitor him for any of the above and contact your pediatrician
if you notice any problems.
I hope this helps