Thank you for your query on Healthcare Magic.
Your child have developed a hematoma
which is a collection of blood on forehead due to the injury.
Nothing to worry as there are no symptoms of concussion
But watch for vomitings, seizures, bleeding from nose and ears, abnormal behavior, drowsiness
,and any decreased limb movement.
If you find any abnormal symptom or sign, consult emergency immediately.
The swelling usually decrease gradually.
Physical examination by the pediatrician
is important to look the swelling for any underlying bony problem.
Hope I have answered your query.