Thank you for your query on Healthcare Magic.
Your child seems to have developed mild concussion head injury
due to the hit.
and hurting stomach (due to nausea) is due to head injury.
Little red spots om hit area is due to bruising caused by the injury.
Nothing to worry as the child is calm and behaving normally.
Watch for the following abnormal features and if you find any report to ER immediately.
3.Bleeding from nose or ears
4.Loss of consciousness
or altered sensorium
5.Paucity of limb movements.
For headache you can give Tylenol in prescribed dosage.
But consult your Pediatrician
for the examination of your child to look for any abnormal signs and their management.
Hope I have answered your query.