Check that it's not bleeding. If it is, clean it asap. If there's loss of consciousness, dizziness, drowsiness or balance problem, bring him straight to the ER as he may have had a concussion.
Also don't forget to apply ice (wrapped in a towel) to the bump asap. But if there's bleeding always bring baby to a doctor.
Thank Nalika! This is helpful
Where are you from ??
Rajan Gupta