Thank you for your query,
The swelling is due to formation of the hematoma
in scalp layers on th skull bones.
The headache is due to impaction
of the trauma on brain.
But the child needs neurologic examination by your Pediatrician
to assess for any abnoraml findings of brain involvement.
For headache you can give Tylenol
in prescribed dosage.
Observe for next 24 hours for any vomitings, abnormal behavior, seizures and if you find any consult emergency immediately.
Hope I have answered your query.