on head of any child is always riskful.
becouse without symptomes we cant judge the severity of injury as the child doesnt tells much more .
if the injury on head is associated with vomiting
/ unconciousness is dangerous . if symptomes are like this immediatly go for CT scan
Internal injury can be ruled out from CT scan of head
So i will advise you to go for atleast one check up by the surgeon / paediatrician