Thanks for your query.
Head injuries on frontal region sometimes leads to hematoma
formation over eyelid which is due to bleeding from superficial vessels.
I advise you to apply ice fomentation over affected area,give paracetamol
for pain relief.
Observe for warning signals that is..any abnormal behavior,any bleeding from ear or nose.any vomiting
and in case you report take him to pediatrician
Your son ill be fine.