Thanks for writing your query.
Swelling is common after head injury
due to soft tissue injury
. Lump and discolouration of skin will disappear in due course of time. It is a good sign that your son is active. It means that the injury is only external in soft tissue and there is no damage in brain. You should not worry unless baby is lethargic or there occurs episode of excessive crying, vomiting
, seizures or unconscioussness or bleeding from nose or ears.
I hope this is helpful to you.