Thank you for your query,
The swelling is due to formation of hematoma in scalp layers above the skull bones.
Because of concussion
there may be vomitings after the head injury
These two incidents looking like related.
Observe for persistent vomitings, drowsiness, abnormal behavior, fits, decreased limb movements, and if you find any abnormality
, report to emergency immediately.
If the child is active and no abnormal symptoms and signs, nothing to worry, but consult your Pediatrician
Hope I have answered your query.